visa exempt allows you 30 days. You can extend it once per entry for an additional 30 days. If you wanted longer you could leave the country, either fly or border run to a neighbouring country and get a new visa exempt stamp on re-entry, which would also be eligible for a 30 day extension.
Get a Multi Entry Tourist Visa. You get 60 days each time you enter Thailand, which you can extend by 30days for 1900B at immigration. You then leave the country and re-enter for another 60days +30ex. You can get up to 270 days with this if timed perfectly. Add in 2 land border runs (use a company) +30 ext. and you've got your 12mths.
Alternatively, ED visa is your next best option. Or possibly dodgy 1yr "business visa" that I've seen visa agents offer in the past. Idk much about it or if it's still a thing though.
they keep posts open, you will get more answers but a mix. Some helpful, some not so. I'm a member of both, if I want a correct answer on a Visa question I ask here, general spit balling questions are probably better in the other group.
get the 30 day extension, if you want more time after than, use a border run company. You can get 2 visa exempt entries by land per year. Get an extension on each of those and you've got an extra 120 days. You could do the same next year. But after that you've gonna need a proper long term visa if you want to stay here
Get the METV. So there's no limit on visa exempt entries, but it's issued for tourists. It's not designed for living here and that's why you'll encounter issues eventually.
So whilst there's no law, 6 months staying here is a good general guide for when you might encounter issues. Probably some questioning and a warning to get the correct visa or you'll be denied entry next time, rather than being denied straight away. But it's up to the IO, so no guarantees. Land border crossings, with a border run company is the safest method. They will check everything and won't stamp you out unless you will get stamped back in.
You can just enter visa exempt if you can't meet the requirements. Some embassies have more requirements than others, but the ticket departing is pretty standard.
It's actually a requirement to enter Thailand on a Visa exempt entry as well, it just very rarely checked by immigration.