Unfortunately it's not you think, it's what they think lol, the TM30 is used in many of the visa processes. But you say you got the visa without it, well done. If you do need in the future you would need to talk to the immigration office and explain your situation they will tell you there requirements.
there is a "residents certificate" form, it's in Thai , you get it from the imm dept, it needs the house owner to sign it, you need a copy of thier blue book and Thai ID.
Retirement is you have to have 800kthb tied up in thai bank for 2 months before, and 1 month after, then 400kthb for the year. Support of a thai child you need 400kthb in the bank when you make the submission, but the application takes 30 days because it's sent to Bangkok for approval (if your outside) so best to keep it above 400kthb during this. Paper work will require extra for the Thai, berth certificate, blue book for the child. But it can vary office to office so best to check.
There are several restrictions in place depending on how you send your money, if you use Wise or similar you can only send over 50k to the top
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banks like Bangkok bank and KBank. Your bank will probably have a restriction on your account as well which you can ask them to increase based on your credit risk.