I've been searching for this information for awhile now, but haven't been able to find it.

I have a US passport, and arrived in Thailand with a 45 day tourist visa. Once in Chiang Mai, I got a 30 day extension at the immigration office, which expires at the end of Dec.

From reading the posts here, it seems it's not possible to do another visa extension?

I'd prefer to stay in Thailand until the end of January or February, if it's possible. Otherwise, I don't mind going to Vietnam or Cambodia for a week or two (I'd spend at least a week there), and come back to Thailand.

Thank you!