that is not correct. You need Covid insurance till your O visa expires. If you only have one month insurance immigration will only stamp you in till the date which your insurance expires
Just like Stuart says. When you reenter Thailand with a reentry stamp Day 1 starts all over again. BUT you have to report to immigration office within 24 hours of your arrival. Then you will get paper in your passport with the new 90 day report date.
I got a new passport at the Belgium embassy in Bangkok. They also gave me a letter to give to Thai immigration explaining the reason for the issuance of a new passport. Take your old and new passport to immigration and they will transfer everything to your new passport.
The passport you arrive in Thailand with is the one you will use when you go somewhere that your passport is required. Such as immigration. You cannot use the other passport that does not have an entry stamp and