Yeah you can't go too wrong by just turning up and sorting yourself out at Railay/ Tonsai. If you're flying in to Bangkok, pre-book a flight (return!!!!) on AirAsia (
www.airasia.com) to Krabi and then take the bus/ longtail boat combo (about 1100Baht I think) to get to either West Railay or Tonsai. Plenty warm enough to climb or DWS, but be a little careful of simplly paddling out to any old rock (esp an island) as some are protected by gun-toting locals who have the rigghts to climb the cliffs and collect extremely expensive "swallows nests" for a regional delicacy...ask about at one of the several climbing shops there as to wear the best DWS is, and what the tide charts are like.