We've had a great experience with http://gulfchartersthailand.com
which is the newer site for Yacht Charter Thailand
Had no interest in the Pukhet area and the associated crowds. Chartered out of Koh Samui, spent over a week in the marine
sanctuary (west of Koh Samui - Koh Phaluai and Koh Mae Ko) and then around Koh Pha Ngan. Beautiful secluded bays when desired, awesome inexpensive food
ashore, and loads of helpful hospitality when we chose to be in civilization. Most days we didn't see any other cruisers / charters; depending on the area the fishing
boats were out.
May was a bit on the warm side, especially when we visited as it was one of the hottest months on record
. Still, the experience in the area and the unexplored opportunities aplenty. Great combination of activities and convenience without the full commercialization and catering to tourists and cruise
Depending on season they move the boats to Koh Chang, which is offers even more remote
areas to cruise
. Chartered there last year and wouldn't hesitate to go back.