@Bryn *******
, No need for 800K in a Thai bank account if OP applies for his Non-O based on retirement in another country. But yes, he needs to have funds of 800K thb in a Thai bank account if he applies for an initial visa in Thailand at the local immigration office.
You cannot use the monthly income/transfer of 65,000 thb method for the in-country initial visa application or the very first 1-year extension application. You need to have banked money for them.