I'm currently in the Caribbean with our 4.5 month old. She's slept in the buggy each evening while we've had dinner and everyone in the hotel knows her, she's a little celeb. It has been the best break for me ever. I've nearly finished a book and done yoga every morning. We've taken her swimming without the hassle of a London commute. And best of all her daddy has spent loads of time with her. Definitely book something! She's been a bit grumpy when it's been really hot but I've just retreated to the cool room for a while.
We found our hotel on Mr and Mrs Smith, they're so helpful and called the hotel to check babies were allowed. We've never had a disappointing hotel when booking with them.
Another company that looks great but I've never used is Baby Ftiendly Boltholes -
http://www.babyfriendlyboltholes.co.uk
They flyered BTC a few years ago.