sure or not?
Ok for thailand, u can try koh Tao, koh phangan, koh lipe, koh chang, koh lanta...etc.. more commercial island will be phuket, koh samui, koh samet..etc which is well known among sinkie.
Go for the former, Koh tao (for diving) or koh phangan (relac island). Or Mae hong Son province, PAI, heard very beautiful there.
U can also try laos, luang namtha, luang prabang, vang vieng (for tubing), vientaine ( capital) , paske, 4 thousand island...etc
laos many many mountains n water fall, if u adventurous enuff. take a ride along the mekong river.