Ko samet by treetop2000
a great place to visit, just a few hours out of Bangkok (more if by bus). so it’s not an epic to get back to bangkok in the evening the next day— a good weekend trip, popular for people from bangkok.
I like a beach to have hills in the background so a few hours more (or a quick flight from Bkk)then your in Koh chang
This website (not mine) gives a bit more ideas about ko sumet: