It's been several years since I was in Krabi, Thailand... back before the big tsunami that did so much damage to the region. I understand that the area is getting back on its feet, and that tourism there is once again good. In fact, a trip to Krabi can help to boost the area's economy as it recovers from that devastating storm.
Krabi is a wonderful place to snorkel. We hired a boat just for ourselves, and it was very affordable. It can be managed at any of the little stalls on the roadside near the beach, or it can be done from one's own hotel. I preferred the packages (and prices) from the little stalls by the road. Alternatively, you can book a spot on a diving boat, which we also did for one of our snorkeling trips. It is different from booking one of the little boats because you'll find yourself in much deeper (and rougher) waters)
The waters around Krabi are amazing. There are several small islands off the coast, making for lots of sealife to be seen there. The drop off at some spots can be pretty steep. At one point, we were encountered by what seemed to be a black wall in the water. That was where the sea floor made a dramatic drop. As we swam closer to that black wall, the water got cold. We turned back without entering the deeper waters, to be on the safe side (and at the advice of our boat operator), but it was an eerie experience to see the waters in that state, and feel the cold of the deeper waters creeping over the whole body.
One of the things I really enjoyed seeing in the waters of Krabi was the starfish. There was one attached to the cliff face of one island we'd stopped at with the diving group, and it was no less than five feet from tip to tip. It was a bright blue color, almost luminous, that contrasted beautifully with the brown and red of the coral to which it was attached on the cliff face. It's one of those pictures that I will keep in my mind for a long time.