Since you said bangkok, I'm assuming you're interested in visiting asia.. may I suggest Amanpulo in the Philippines?
I've been to Palawan before and there's just something magical about that place.. ALTHOUGH I haven't been to Amanpulo (opted to stay at another resort in the area). I've been reading a lot of good reviews. So much can be said about the beaches of Palawan, the casitas or bahay kubos with the view of the ocean, but Amanpulo stands out because of it's service(i think it's their guest to staff ratio)
Weather wise, it's still pretty hot in May so you can still catch some sun and it's not as crowded unlike easter season (but then again, easter season is earlier this year). I think you get a few raindrops, but not so much to actually ruin your whole honeymoon.