Ko Lipe is an island way,way, down south in Satun province, next to Malaysia. In fact if it was any further south it would be in Malaysia, Langkawi island is just on the horizon. The island is fairly small, and you can easily walk across it in 15 minutes or so. It has some of the best off the beach snorkelling in Thailand, and a short boat trip will take you to even better spots on nearby islands.
No jetskis, banana boats, full moon parties etc, but a great place to relax.