In reply to Will Mortimer:
You're in luck. While Mahidol is a bit out of the way, the west bank of the Chayo Praya has more than its fair share of gyms, and Don Muang airport is accessible for flights out. There's no shortage of things to do. Bangkok is one my favourite cities - ignore the naysayers.
Finding climbing partners is pretty easy, especially in the peak season when you are there. Not sure about Chiang Mai climbing at the moment as there were rumours of a closure a while back.
Another option is Laos, inland from Tha Khaek, where a German couple started up a climbing guesthouse and bolted a lot of the valley walls on either side. Green Climbers or something like that. The trains and busses through Isaan to Nakhon Phanom and on to Tha Khaek expose you to the heart and soul of Thailand so worth it on its own - but I've flown there from Bangkok a few times so it can be done even quicker.