Which Thai Islands for mid-May honeymoon?

My fiancé and I are all set to honeymoon in Thailand and Vietnam in mid-May to early June. We want to do some adventuring but would also like some relaxing, drink-in-hand beach time in Thailand at the start of our trip (overwater villas, anyone?). May appears to be the start of rainy season everywhere, but especially in the Andaman Sea, which makes me feel like we should rule out Phuket and Krabi and head to Koh Samui or Ko Tao. Thoughts or suggestions? TIA