@Mark ********
your options depend on your age, if you have Thai family and many other things. You haven't given any details to answer your question.
You can purchase a tourist visa before you travel and receive 60 days when you arrive. You can apply for a 30 day extension.
Then do a border bounce by leaving and returning and get a visa exempt 30 day stamp and apply for a 30 day extension. That's 5 months.