well, I know nothing about Thailand. You can always try and check with dive ops to see what they have, you might find one that has other tanks available and perhaps that would influence who you decide to dive with, though it would hardly be the most important factor in selecting a dive op.
Beyond that, well you use what you use. Time and practice will help. Fitness, good bouyancy control and being comfortable and relaxed help. I'm sure there some old threads around this board with ideas on how to work on it.
By the way, you might want to fill out your profile info with where you're from and all that good stuff.