Southern Thailand is wonderful, but a bit touristy in some areas. For a fun alternative, try a bike tour with http://www.greenbikingclub.com.
They are based in Khao Lak and do 1/2 day to full day bike rides. We recently went on one of their full day excursions and had a blast. The ride leader was super friendly and - being from the area - was able to take us off the main roads and introduce us to the real Thailand.
We talked to farmers in the rubber and oil plantations, had authentic food at a roadside kitchen, visited a village cooperative making bamboo furniture, went swimming at a spectacular waterfall ... those are just a few of the highlights.