Bkk To Trat Or Better Somewhere Else?

On Thursday or Friday I need to make a Visa Run from BKK.

Actually my better half and I got the idea to brake for a few days, maybe till Tuesday.

As I only know Cambodia for Visa runs I thought going there and than to Trat (or maybe Koh Chang).

But if there is any better solution with beach I am open to that (just my wife can not leave country because she need to take a new passport first).

So if it is Trat (or Koh Chang) or something else you may recommend.

We would like in a relative cheap resort (prefered bungalow) with AC, and my wife wants enviroment friendly with a lot of plants and if work under the "sufficiency economic" model she would love it even more.

While I want to go diving with a dive center somewhere near.

Anyone has a good idea/recommendation?

Edit: for improving spelling and grammar