What goldengloves said or Phuket, and live in the Rawaii area. Koh Samui sounds very similar to Phuket. I think Phuket is 450km squared so there is alot to explore. Rawaii is a real laid back reggae area so you will be able to concentrate there.
One thing about Thailand you need to know is everywhere can be nice and everywhere can be awful. For example Bangkok is very cool, many things to see, great shopping, cheap taxies and there is some really nice beaches outside of it. But BKK can be shithole if you go to tourist rat holes like Khao San Road, or sit in rush hour traffic.
In Phuket, Patong is a dump, but Surin is very nice! Every place you will ever read about it, or talk to anyone about will have mix reviews. You need to be open minded when coming here also. Many tourists blow through here, treat the locals like shit, and go home saying the Thais are awful... but in reality its them having no respect for the people. The effort you put in with people, will pay you back 10 x fold.
Regarding Phi Phi you can live there! There's 116 hotels as far as I know (go look on Agoda). Maya bay is a national park so you can't live there, but you can camp the night there though
