Oh, hello beach!
Before we went back to Sweden again we spent New years at Koh Samet just relaxing in the sun and waves. Koh Samet is quite close to Bangkok so it is very convenient if you don't have time to travel further south. Just take the bus or taxi about three hours south, then jump on a ferry and you are there.
We were staying right at the beach at Ao Cho Grand View which we really enjoyed. The beach was nice and clean and the water warm and turquoise. This island is packed with little hotels for various budgets, but keep in mind that this island is quite small and it can get quite crowded, you will not get the beach to your self. On the other hand this island is just perfect for relaxing and get some sun on your nose and eating fresh sea food.