For 5 week stay, I used money supermarket. Clicked "preexisting conditions" filled in the on line info and it gave me several to chose from. I'm not sure for longer stays but a Thai policy might be better.
If your embassy supplies the affidavit on the 65k I think you can.
Otherwise I think you'd have to use the 800k for first year extension whilst also transferring the 65k in monthly. Then switch the second year to the income method. Think I've said that right. 🙄
Get the non-O. Go open a bank account asap once you arrive. Might need to check what paperwork they want. If you have a Thai friend can go with you that helps. The point us with Non-O you'd need to deposit 800,000 tbt to get the one year extension. If that's the time you'd need. The non-OA doesn't need the money in thailand. So it may suit you. I'm so sorry to hear of your brother's death. What a terrible time for you.