there's no difficulties opening an account when on a non-O. The non-OA doesn't require a bank account but is linked in date to the insurance. Which can be costly and not very good.
You've got a bank account. You put required money in bank. Head to neighboring country, apply Non-O retirement e-visa ( NOT O-A ) and use entry stamp with accomodation booking to prove you are there. Re-enter Thailand and do 12 month extension of stay. It's been explained by others too.