Thanks for all the replies guys.

Koh Samui and Nha Trang are out. Samui I was just at relatively recently (at the amazing W Retreat) and Nha Trang is in Vietnam which, after an awful experience travelling to Vietnam a few years ago (got mugged and luggage stolen in two separate events), I don't want to go back too soon.

The more I think about it, the more Bali makes sense. The Westin looks nice. It's about the cheapest place for me to fly (I live in Perth, Australia and flights are like $300 return) and it's close to Singapore where I may need to travel on short notice for something during that time period.

Langkawi still sounds good though and I'll look into Fiji.

New Caledonia also popped up - thoughts?