The non-immigration type O visa is valid for 1 year and can be extended for 1 year at a time in various way. Over the years, I have used 2 different methods to extend it :
Family reason - easy paperwork, but you need either THB 400K in the bank for 2 month or certified monthly income of more than 40K/month.
Work reason - difficult paperwork, but you just need 40K/month salary.
Here is a 2 year old example of a Non-O "Thai Wife" visa extension
Let me say that it is in general VERY difficult to find precise information on process & required documentation - the official immigration web pages are a disgrace and you will inevitably be blamed for your preparations even if there is practically no way you can know for sure what you need to prepare.
Even the frustrating experiences that most aliens have had no doubt, mostly you are actually treated both friendly and with respect by the immigration officers and over the years both attitude and environment have become better (at least that is true for Nonthaburi Immigration), however they DO have to check you and it is your responsibility to deliver the correct paperwork.
Extending Non-O visa based on family
Documentation requirements : (in the order as below - you WILL be blamed if your documentation is in the wrong order)
Visa extension form TM.7.
Copy of your passport.
Copy of Marriage Cetificate.
Copy of spouse I.D. card (I have the backside of the card on the copy as well).
Copy of spouse house register including any children.
Copy of childrens birth certificates if you have any.
Money requirements : either option 1 or 2, whichever you prefer
Bank account statement going 2 month back showing that you have never had less than 400,000 baht in your account the last 2 month (my statement was from 6 days before I started the application process and was accepted and I was told that 7 days is also ok). You go to your bank and ask them to make the statement, it cost 100 baht.
Copy of your bank book that have been updated on the SAME day as you start your application process. You also MUST have a transaction on that day, eg. last time I went the 19. february and I updated the bank book on the 19. february before going, but since the last transaction was the 18. february, the immigration cannot see that it was updated on the 19. The solution was for my wife to transfer 100 baht to my account and then go and update the bank book again.
Income or Pension more than 40,000 baht/month certified by your embassy (or consulate) in Thailand (I haver never used this option under family based visa extension).
Map to your home (I have a well drawed map in thai, but maybe a google map would be ok).
Family photos : all family members must be in all pictures (in my case : me, my wife & our 2 kids). I copy the pictures to computer, add them to a word document (2 pictures on each page) and print out the word document. Typically the picture requirement is 6-8 pictures but I come with 10 (sometimes they will complain there are too many pictures, sometimes that there are too little pictures, though with 10 pictures never complain about too little)
Outside the house in front of the house number - the house number must be very clear and easy to see.
Outside the house but zoomed out so most of the house is visible (I always include our 2 cars in that picture to give the impression that we are not poor).
We include a terasse picture but I don't think it is necessary.
Picture from the living room (you should include the TV).
We include a picture from our activity room which looks expensive, not necessary but I think it helps.
Picture from the kitchen.
Picture from my wifes working station.
Picture from my own working station.
Picture from the bedroom (again include TV if you have a TV in the bedroom)
Picture from dressing room or from your dressing closet with your dressing closet doors open.
Earlier years I prepared 2 set of the document requirements : 1 set with copies and 1 set with originals, however this year I had to prepare 2 sets of the copies and then have all the originals available in a separate set.
Prepare all required documentation.
Go to immigration with your spouse and queue up to get your paperwork checked (you show only a copy version of your documentation).
If your paperwork does NOT check out, you need to go home and remedy it.
If your paperwork DOES check out, you will get a queue number for detailed evaluation.
You wait until your queue number is called and then you & your spouse go to detailed evaluation. There will be a single officer and if the officer is experienced there will be no other officers involved.
The officer will ask different questions while inputting various information into a word document on the computer. The meaning of the interview is to snoop out any problems especially if you are faking the marriage, eg. are you in fact living together. If you are legit you don't need to fear anything even if you cannot remember how many years you have been married. The interview took I think 20 minutes last time, but while waiting in queue at least one interview before me was an hour long.
At the end of the interview you are asked to pay a 1,900 baht fee for which you will get a receipt.
You will be sent out to wait for biometrics (in my case only picture, however I saw other people that would have to take finger prints, but maybe they already had mine from my vacation to Denmark a month before).
I got some papers I had to make a copy of (at Nonthaburi Immigration there is a copy service outside the building). It is unclear why they think it is cheaper to let me pay the copy (15 baht) than taking the copy in-house and avoid the overhead of me running in and out of the building resulting in changing aliens in the workflow - there is nothing you can do about it could also be that there actually is a good reason.
I come back with the original and the copy and an officer brings it to the back (there the original came from) and are then told to wait.
They call my name and give me my passport with a stamp that my visa extension application is under consideration. I have to come back a month later on a specific date and even on a specific time 15:00 (they have never told me a specific time before).
Visa is under consideration (here an older stamp for security reasons).
Consideration number : 935/60 - you can call the immigration and reference this number and ask if the final visa is ready
ภรรยาไมย: they call this visa "Thai Wife"
28 Mar 2017 : the date I have to come back in person to get the final visa stamp (if approved but it always is). You should call first using the above reference number to be sure that the final visa is ready - often it is not.
Ok, finished this time. Just need to wait a month.
Problems I experienced last time :
House number could not be read properly on the pictures (my fault).
Missing picture of our bedroom (maybe my fault, however I could not find official information on the picture requirements and last year they did not want the bedroom picture and also I don't like them to snoop in my bedroom so I tried without).
My bank book was updated the day before I started the visa application - it MUST be updated on the SAME day (my fault as that information is available on an official website).
The person checking out paperwork reordered it and our detailed evaluation officer complained it was not in correct order (this is out of your control, there are nothing you can do).
The copy service outside of the immigration building had mixed up some passports and a man was waiting there not able to get his passport, I guess another man had left with the wrong passport (not my problem but nontheless a bad situation).
Extending Non-O visa based on work
I have done the work based visa extension for many years, partly because I was actually working (in my wifes IT company) and partly because we mostly did NOT have the 400K (nor the 40K monthly income from abroad) required for a family based visa extension.