Paul. You might like to try P&O.
We used to use them a lot. Stopped when the ships got so large. A friend reported back on a Caribbean cruise with them recently - sounded like the worst of Brits Abroad.
We have become fans of Star Clipper (up to 200 passengers and under canvas) and of Regent Seven Seas - up to 700 passengers and all inclusive - not too expensive when you compare their discounted prices with the all in costs of P&O etc once all the trips, bar costs and tips have been accounted for. We used to really enjoy Minerva - especially the top historian speakers - but they now use the same trip agents as every other cruise line (they used to do it all themselves) and have put their prices up by too much.