I really agonized about where go for the beach-y part of our trip. Miu Ne? Nha Trang? Koh Rong in Cambodia? We eventually settled on Phu Quoc, a Vietnamese Island that is located in the gulf of Thailand.
It turned out to be a terrific spot. Even though we were there right over Christmas, it wasn't very busy. A new airport opened just before we flew in, so it apparently will get much busier in the next few years. But for now, we were able to get a little place, just a short walk away from a beautiful beach for a very decent price.
One day, I sat by the water and read a whole book. Another day, we rented a motorcycle and zipped around the island. The rest of the time, we napped, read, restaurant hopped, and swam in the warm water. The only blight on our time in Phu Quoc were nasty mosquitoes, but not much you can do about that.