It's been a while since I lived in Singapore, so my experience is pretty dated. There are a lot of places to consider though. As much as I love liveaboards, after 11 days on Peter Hughes one of the islets in the area would look pretty appealing to me. Sipadan used to be my first choice--when you could stay on the island. The Sangalaki--Derawan--Kakaban combo, also off Borneo, was also good. Terengganu, up Peninsular Malaysia's east coast, is worth looking at as well. Layang-layang is (used to be?) good for a short stay. Does Peter Hughes disembark on Bali? I'd be tempted to stay (or go) there for a week. Bali has a nice variety of diving available. As indicated above, the Andaman Sea is out of season in April, I think, so plan on diving east of the Malaysian/Thai peninsula.