Can I apply for a Non-O visa in Thailand after entering on a tourist stamp?

Make sure to have sufficient funds in your name on a Thai bank account. Come in on a visa exempt. At immigration go for a 90 days non o based on marriage. I have done exactly this in Bangkok a few months ago, basically you start all over but you can certainly do it from within Thailand if married to Thai national. After the 90 days you go back to the year visa.

For what it's worth for the future, I always get a single entry reentry permit whether I plan on using it or not when I do my annual extension as I'm afraid I'll forget.

𝘁𝗼𝘁𝗮𝗹𝗹𝘆 𝗳𝗼𝗿𝗴𝗼𝘁 𝗺𝘆 𝗿𝗲-𝗲𝗻𝘁𝗿𝘆,

Ouch, that was a massive fail 🙁

Forget the apply for a tourist visa online route you're coming back way too soon to fool with that

You can come in on a free stamp 60 day entry, then go to your immigration office and see if you can apply for an in country 90 day Non-O visa based on marriage to a thai (while most offices can issue in country Non-Imm visas some do not, so you need to check)

If your office can issue Non-Imm visas. Then apply for the 90 day Non-O for 2000baht, wait the under review period, go back get the Non-O visa and new 90 day stamp inked in then wait until you have 30 days or less left on that stamp to apply for the year extension.

My advice is dial back the paranoia just a notch or three 😛 you're far from the first person who left on an extension without a re-entry permit, lost it and had to start over from nothing 🙂

Best of luck with it