What are my options for returning to Thailand after leaving without a valid re-entry permit on my retirement visa?

Okay the first mistake was thinking that the Non-RE you got written on your entry stamp meant anything other than you used a RE-ENTRY permit to get back in 🙁 That's all it meant, nothing more nothing less and you should have been stamped in until Feb 2023 like your extension was valid for.

The FATAL mistake 😮 <- as it pertains to your extension 😕 was NOT buying another single re-entry permit when you left the country in May 2022 🙁 because stamping out without a valid re-entry permit in your passport is what cancelled your current extension.

You are correct, you either buy a new 90 day Non-O visa from the thai consulate in the US using the eVisa online program (which means you meet the requirements for that visa THERE <- meaning you need mandatory insurance). Enter on it, get stamped in for 90 days and then apply for the year extension like normal at the immigration office

OR

You come in on a 30 day visa exempt entry stamp <-(there is no 30 day tourist visa, you're talking about coming in on a FREE visa exempt entry). Then you get your act together and immediately go to your immigration office and apply for an in country 90 day Non-O visa for 2000baht (which does NOT require any insurance BTW). You wait the under review period, get the Non-O visa and new 90 day stamp inked in and then get the year extension for 1900baht after 2 months.

The only mess was that you didn't get another single re-entry permit before you left in May 2022, believe me you're not the first person to have done that and cancelled their extension when they stamped out.

Those are pretty much your options good luck with it