I did my first trip to Thailand this past may. I am in my mid-20's We hit a few of the islands including koh phangan, koh samui, phi phi, as well as Krabi and Phuket. My favorite was koh phangan-( mostly known for the full-moon party.)..however, we went during another time of month and loved the relaxed Island feel. We rented scooters for $8 a day to get around the island to explore more secluded beaches. Everything on the island including Lodging/meals were pretty cheap. Well under $200/night. You can fly into koh samui and take a fast ferry to the island. If using points the hikon koh samui is a great value. Let me know if you have any other questions.