Most of the places mentioned will be tourist central at that time of year. If you're fine with that then OK. There are still some spots that are not overrun though. If that's want you want, then look for smaller beaches or more exclusive resorts on say Phuket, that are not too difficult to get to. The downside is that there will be less to do in those locations. Fewer restaurants, fewer beach and activity choices. Some Thai beaches are not great for swimming.