Hi People... Spending 3 weeks in Thialand in Febuaury.. Best places to go?

My partner and I are looking for great beaches.. Keen to see the top "touristy" destinations (Phuket, Bangkok, Ko Samui etc), to tick them off the list.. But more interested in beautiful beaches/fabulous beach huts off the beaten track, places not so touristy and a little less commercial..