In reply to Elia:
I did a very similar trip not long ago there's a place about three hours North of Bangkok I climbed at that was pretty good
http://namphapayai.camp/rockclimbing.html . The place just had a really good relaxed atmosphere and even a zip wire approach to one of the crags, it doesn't have as much climbing as some of the islands in the south or as Chiang Mai but it's a really nice place and less well known.
There's not much climbing in Cambodia but if you did want to climb there check out
http://www.climbodia.com/ , the guy who runs it is great. I can't speak to much about the climbing as when I was there he was just getting setup and only just got a crate of bolts through customs to start putting up routes. The four that were up when I was there were good, worth emailing them to checkout what else has been put up as he was keep to develop the area. The area it's based in, Kampot, has great food. Ask the owner of Climbodia to recommend an Indian place to eat, I can't remember the name of it but it was his favourite in the area for good reason.
If you go in the peak tourist season (Nov / Dec to Jan / Feb) finding climbing partners is easy, outside of that it can be trickier though.
These are all places I plan on going back to, hopefully I can convince a friend or two to come along too.
