What are my options for extending my stay in Thailand after my tourist visa expires?

Leave the country for a couple of days and return kick start another 60 days..

I don’t see why you are worried so much and so early. You now have a tourist visa, not even a visa exemption. After using this one, you can go to Laos to either do a border run or apply for another single-entry e-tourist visa. I’d recommend the latter, which I did a few days ago after “abusing” the visa exemption privilege multiple times and getting denied entry, given their tightening control over visa exemptions. By the way, next year they probably won’t count your previous year’s entries in the total number. Either way, you will not break their rules. Also, they may be more chill during low season.

What is the valid until date, or enter before date on the Visa? If you re-enter Thailand just before that date will be given another 60-day stamp which you can also extend another 30 days, effectively getting 9 months out of the visa.

Have a week holiday in Vietnam then fly back with 60 + 30 days again

A 6 month METV works like this

you can enter/exit thailand as much as you want during the validity of the visa itself (you said yours is Sept 2025 to Mar 2026) Each time you enter you get a 60 day entry stamp. You can extend each entry one time for 30 days for 1900baht at the immigration office if you want to

When your stamp runs out you need to exit/re-enter the country and you will get a new 60 day entry stamp <- you do that as long as the visa is valid for.