Any cruise line other than thomsons will use different airlines. We have in the last 6 months flown with them and on longhaul they are much improved with very good legroom and seat back screens we were impressed compared to previous flights with them. Cunard do carribean cruises and if you dont want formal try ocean village.
RCI/Celebrity only use scheduled carriers like BA, AA, Delta, Virgin, Continental etc. Try them. [Exception being their private charter to Santo Domingo for the Legend and Vision ships.
We have just returned from the Caribbean with Thompsons and it was one of the best flights we have had. The Seating is excellent with TV's in the headrests and the food was also good. Crew excellen.