If you are going to st lucia, be sure to do the "cosol" tour...best value for money we have every had on an excursion. full day trip with food and drink supplied all day for 50 dollars. google in cosol tours and you will find all the details.
We went on Ocean Village Caribbean cruise 2 years ago and did our own thing in all ports of call,had no problems whatsoever,you can pick up a cab at the port,tell them what you want to do and where you want to go.Cost for about 4 or 5 hour tour was about $80 for up to 4 people so it pays you to share with other like minded passengers.The only place we went on organised tour was Rainforest canopy trip on Dominica(not sure if you are going there).It was a very good trip but we could have done it cheaper if we had done our own thing.
We went on Thomas Cook Airlines from Gatwick and we were told on arrival at airport the seats had already been allocated to us and we had the same seats coming home.
Hope this helps,any more questions please ask.