The island is also known as Koh Kut, located 1 or 2 hour with speedboat (cost about 900 Baht) or 3-4 hours with normal boat from Bang Bao Bay. A place much more solemn compared to cheery Koh Chang.
The island lies close to the border of Cambodia and there’s literally no nightlife there, making it a family friendly island.
Recently, a British journalist wrote about Koh Kood, calling it Thailand’s last unspoiled island. With that kind of publicity, undoubtedly the status won’t last for long. Better to go there now before deserted beach aficionados start to flock there.