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As mentioned above by dumpsterpurrs the Similan & Surin Islands are the better spots to dive, but the season is closed at the time you wish to travel. I would recommend Koh Samui if you wanted an Island at that time. It has some very nice resorts like the Intercontinental Hotel which has beautiful sunsets up on the hill overlooking the ocean. Very romantic if you're on your honeymoon. There is a speed boat that can go out to Koh Tao each day. Long trip, maybe bumpy, but two dives with lunch, best dive sites around. Or cheaper option is to stay on Koh Tao itself. You would have to fly into Koh Samui then ferry out. You could do both, start on Koh Tao & finish on Koh Samui for a few nights. Hope that helps.