I would like to use Avios to fly into St Lucia and then onto another island. Would love to try out St Maarten (I know BA doesn't fly there) but can't find any direct scheduled flights between them two. BA has some 5th freedom flights in the Caribbean but they only fly to St Kitts from St Lucia right?? Ideally I would like to fly LGW-SLU-SXM and then back to the UK. So from SXM what would be the best and closest island to hitch a ride back on BA to LGW?

This would be for November. Any other suggestions?