Hi Leah, the only one I know of is the Spanish Pullmantur cruises.
They have one ship in the caribbean, the others in the med. I was tempted to do one of their caribbean cruises, but don't know if there would be any other English speakers on board.
I did ask a question about them lower down the board.
Will be interested to see if you have any luck.

thomson are going to caribbean this winter and you can pay to upgrade to all inclusive on there.