This was in Chaengwattana, Bangkok. From what I have read on this forum they usually don't ask for a letter there. Different immigration offices have different rules. Probably better to bring a letter if you can get one?
I'm in the same boat as you. Did a covid 60 day extension today at chaengwattana in Bangkok. When it was done I told the immigration officer that I am saving up for the 1 year marriage extension, but it's gonna take a few more months, and asked if I could come back in a month and do a new covid extension in a month prematurely, she said that would be fine. 🙏
If you do the same and go late November you will almost be in February. Then you can do your 60 day visiting family extension, and be in mid /late April. 👍
Didn't have to show any insurance. Queue was about 2.5 hours today, and it is worth to mention that the internet queue counter that shows when its your turn was about 4-5 minutes behind the actual queue numbers, be sure to enter BEFORE its your turn. Not sure if that is normal as it was my first time going there. Good luck!