Which beach to visit?

Hi!

My wife and I are planning a 4 week SE Asia trip Nov 20 - Dec 20. Starting to figure out the bulk of the trip but looking to book flights in and out of the region through Bangkok (seems like that's the easiest and most convenient hub?). Looking to keep our trip to 2 countries so as to not jump around too much.

Anyway, looking to end our trip with a few days at a beach in Thailand before heading back to Bangkok for our flight to New York. Looking for something that isn't crazy touristy but still beautiful with accommodation that is more in line with eco-tourism rather than a Hilton resort. Oh and also we're both vegan (mentioning just in case that changes anything).

From first glance I've been eyeing Krabi...

Thanks!!