Only just seen this:
I would stick with Barbados. There is some really fun nightlife, with a low fogey quotient, especially at places like http://www.harbourlightsbarbados.com/
Some great restaurants, but of course you’ll spend most of the time on the beach – though you could pop out and visit Concorde http://www.barbadosconcorde.com/
A round island sunset cruise is a fun – just ensure you choose your boat carefully so you’re with the right “sort” of people, and you’ll have fun!
If you do visit Barbados, hire a mini moke from http://www.stoutescar.com/vehicles.php and drive around the island; Bathsheba is well worth a visit!
If you ever consider St. Lucia there are some great deals at Sandals La Toc right now (40% off), though it is a bit commercial:
..and they have other resorts in the region.
If you’d had more time to plan, I would have recommended Guadeloupe or Belize….