I am travelling to Thailand this coming Monday and have just over three weeks in Thailand. Once I land I will be heading straight for Cambodia for a week and upon my return travelling to Chaing Mai for three days. Here's where I am looking for info. I am not sure where to go.

I travelled to Thailand two summers ago for three weeks and hit up Bangkok, Samui, Phah Nang, Phuket, Phi Phi, Krabi.

So... I am thinking I want to spend time on a beach for 8-10 days doing nothing but relaxing in an environment similar to Phah Nang or Phi Phi but want to go to someplace new. Any recommendations?