What options do I have for long stay in Thailand without returning to my country for an O-A visa?

Okay, short of going back to your country to get an O-A visa from the thai consulate there, you COULD

check with your immigration office to see if they can do an in country conversion from a 30 day visa exempt or a 60 day tourist visa to a 90 day Non-O based on being over 50 (retirement). AND check to see what the financial requirements are; for instances some offices require the 800K baht to be in your bank account two months before you apply BUT most only require it to be in there on the date you apply as long as you can prove it came from overseas)

IF you can do the in country conversion, bounce out and back just before your current entry stamp expires, getting a 30 visa exempt entry OR go to a thai consulate and get a single entry tourist visa.

Then go to your bank, get the bank letter, compile the documents and go apply at your immigration office to get the 90 day Non-O visa in country. Pay the 2000baht, wait the under consideration period, go back and get the Non-O and new 90 day stamp in your passport. Wait until you have 30 days or less left on that stamp and apply for a yearly extension.

That's how you do it in country with one border bounce to get off the elite entry stamp and on to a 30 day visa exempt entry.