What Visa Should I Get?

Sometime early next year I'd like to take an extended trip to Thailand. I'd like to stay as long as possible. Amongst other things I'd like to do is write a story partially based in Thailand, whether or not I could prove this is my intention or if it could help with getting a visa I don't know.

I am 32 and an American citizen with a bachelor degree in English. Can I get a 1 year multi entry non immigrant O visa here in the USA (This is what I've heard one of the 1 year visas are called), I've heard of a visa you can use for a year that you must leave the country every 90 days to keep valid, if needed I wouldn't mind doing this. What do I have to have as far as documentation or proof to get such a visa? If I am unlikely to get this what's the next best visa that will allow me to stay as long as possible? I have studied Thai for 3 years and am very interested in the language but I'd prefer not to be obligated to go to school as a contingency of any visa I get since I want to spend time writing but as a last resort could pursue that. I did search the archives and while I'm sure this question has been asked many times I couldn't find any threads for someone my age from the USA wanting such a visa.