Koh Yao Noi = about 30 mins boat ride from either Krabi or Phuket. Also completely opposite direction in the country, Ko Kut.

You'll want to visit the Andaman Sea (Western) side that time of year. I would recommend Ko Lanta. Avoid Phuket, Koh Phi Phi, Railay Beach, and even Koh Lipe , as they are now completely overdeveloped and overrun with tourists. That said, November is the start of the busy season, so if you come a little early it might not be as bad.

Ko Phayam, a boat ride from the city of Ranong. I was there 12 years ago and it was idyllic. I'm going back in January next year because it's one of them places that hasn't been overly commercialized! It's beautiful and still rustic.

Santhiya Resort And Spa Koh Phangan. Beautiful and not touristy. Koh Phi Phi don was awesome. More people but fun. Better beaches.

I love Koh Kood and the Koh Kai islands! Been hearing a lot of good stuff about Koh Bulon Lae too, though I've neve been there. Hopefully soon!

Hi - I am also in my thirties and I really enjoyed Koh Chang. And I've heard really good things about Koh Mak, which is smaller, more remote, and right next door. I was going to check it out last month, but as a solo traveler I thought it would be too quiet. For a couple, I bet it would be perfect. Just one ferry between the two islands so you can easily do both. High season starts in Mid November so depending on when you go, you may catch the start of it - but it may not be too bad yet.