What documents do I need to extend my Non-O visa based on marriage with an average income of 40,000 THB per month?

Okay, I am going to make some assumptions here. I assume your visa that expired was a 90 day visa, and not a one year extension, and I am going to assume you rent an apartment/room/condo. If this is correct then you will need a bunch of documents, and in your case the easiest seems to be the financial requirement, as you already seem to have the 12 months of at least bt40k each month coming from out of the country into your bank account in only your name. You can not have zero one month, and bt80k the next, to average bt40k a month. They will not accept that. It must be at least bt40k each and every month. If you have this, then you need a letter from your bank stating that it is your account, and no one else's name is one it. You can not use a joint account with your wife. You also need a letter from the bank showing your full year of deposits each month of at least bt40k. You will need your bank book, and it must be updated on the same day you apply. You can do this by simply making a small withdrawal at the ATM, then put your bank book in the next machine to update the page for that day. You've seen the machines next to the ATM. That is what they are for. Then copy the info page, and all the pages that show your deposits for the full year. Then, you will need the application form, with a current passport photo. A copy of every page in your passport. They might not need every page, but this will save you from having to go make a copy of a page they think you missed. You need both of your original marriage documents, there should be two, and they should have given you two sets of these. I personally make good color copies of both these, and take the originals, and the copies, and give them the copies. It they ask for the originals them give them those. You need a copy of your wife's ID card, and a copy of her name in her family's house registration book. She will know what that is. If she has ever legally changed her name, then you will also need that court document, if her name does not match her name in the house registration book. My wife falls under this, and is one document we had to go back and get the first time. You need a copy of your rental lease, with the name of where you rent on it. Lots of rental lease do not have the name of the place on the lease, so you must get one that does. If where you rent from has ever dealt with a long term visa holders before, they will know exactly what you need. You also need a copy of the property owner's ID card, and a copy of his name in his house registration book. Again who you rent from should know all about what is required. You need pictures of both of you in front of the property, showing the name of the property. A picture of you in front of your room door, that shows the room number, and at least two pictures of you inside the room. All these picture must show both of you together, and you tape them onto one side of A4 sheets of paper. It is okay to take more pictures especially if there are multiple buildings on the property, with a picture of both of you in front of the building you both live in. Lastly, you must make a map showing how to get to your property from the closest main road. They like hand drawn ones, but you can make a Google maps copy, then you put your address on this map. These are all the things myself and my wife needed last May of this year, and the 4th year doing this. The big change in the last year is the financial requirement, and this has changed three times since I've lived here. Originally you could use a government approved condo ownership as part, or all, of your financial requirement, but sadly no more. You used to also be able to use a combination of money in the bank, and money coming in each month to meet the bt400k requirement for the year, but that changed too. Now it is as I stated above, without exception, or, bt400k in the bank. After you get all these documents, and immigration has accepted them all, put them in a binder because you will need all of them next year, with a few of them updated. The updates will be ALL pictures, even though you look the same, and where you live hasn't changed. Of course your bank book, and letters from your bank, and a new application. The rest are all the same, unless your wife got a new ID card, then a new copy of that. This is as easy as I can explain it for you, and I don't think I left anything out. If you are doing this at ChiangWattana then I suggest you get in the queue before 7am, so you are done before lunch. If not you could be there all day. When they accept all your documents, you will get a 30 day wait stamp in your passport, and you come back exactly on that day to get your actual visa extension type O Thai wife. During this time supposedly they check all your documents to make sure they are real, and they could come visit you at where you live, but from my experience, and other friends, they only do this if they suspect your marriage is a scam simply to get a long term visa. There are girls that do this, from my knowledge, at bt5-10k a year. Our immigration lady told us this. I think to see what our reaction was. We have had the same lady process us for the last three years, so she is always happy to see us, and, even though she isn't supposed to, does a little gossiping with my wife now. In regard to the TM30 document. Your landlord should have originally filed this with immigration, and you should have informed them to update it everytime you came back from any overnight, or longer vacation, but, in all my years, and we have vacationed, we have never had them question why there wasn't an update. I have seen other people at immigration suffering from this problem, but personally we never have, and we have never informed our landlord when we came back from vacation. Either the hotels we stayed at never informed immigration, or we are simply lucky, and the officer likes us. This is the only thing I am not completely familiar with, as we have never had a problem with it, but I do know others that have.

Pardon the intrusion, but I think the OP mentioned “average” income and if I’m not mistaken averaging is not allowed. I see you replied minimum but he may not catch that. Sorry if I’m not correct on this.

You show at least 12 months prior the application date a monthly foreign transfer of minimum 40.000 Thb into a Thai bank account in your name, Bankbook must be updated and letters of the bank are needed to verify it is your account and the transfers came from abroad.