Last year did what folks are advising you to do. Entered exempt, then applied for Non-O using 800K in the bank shortly after entering. Do it soon or be aware that there are requirements (not same everywhere) for minimum number of days to be left on your entry when applying. You won't get your Non-O immediately as you do an extension-it has to go to Bangkok for processing. I got a return appointment 3 weeks after my application.
I too was caught out of the country by Covid and lost my long string of extensions. As you won't have a visa or re-entry permit, be sure to be able to satisfy your airline with a ticket out of Thailand within 30 days of your arrival. Either a throw-away cheap ticket from anywhere in Thailand to anywhere outside of Thailand, or a rented ticket available online will do.