For only two or three days I would go to Hua Hin. It is not as touristy as Phuket and much easier to reach. A car from most hotels in Bangkok to Hua Hin is only around 2000 bath one way and takes around 3 hours. There are a lot of car services, just search for hua hin shuttle / taxi / transportation. Hua Hin has some nice restaurants and areas to walk around.