Just you diving or both of you? And where are you?
Many of the threads about diving & cruises seem to be about the difficult logistics - either taking the cruise-arranged "guaranteed to get you back on the boat but don't take you to good diving, assuming it doesn't get cancelled due to lack of interest" or "figure out how to arrange your own at each port so it fits in the schedule." Better than not diving, but sounds like lots of hassle that doesn't sound like luxury to me. (But then huge cruise ships don't sound that appealing to me either.) There's some smaller and luxurious cruise ships out there. The Paul Gauguin from Tahiti comes to mind, they have a watersports deck and even offer PADI certification but I haven't done this so have no idea what their diving is really like.
On other threads I've suggested staying at Young Island on St Vincent. Saint Vincent has really good diving (the small stuff not the big stuff.) Young Island is not Ritz type luxury, it's a private island and a totally different kind of luxury. There are a number of similar really nice resorts in the Grenadines, and there is other good diving in the Grenadines, but I don't know of anyplace else in the region where the nice hotels and the nice diving are convienient to each other.
Look into Hawaii. There's many gorgeous resorts on the Big Island and Maui, including a Four Seasons on each. You'd probably be driving to the dive boat rather than popping out to a hotel dock, but there's good diving to be had.
There's supposed to be a Ritz Carlton coming on Grand Cayman, but not yet.
Hayman Island or Lizard Island on the Great Barrier Reef maybe - haven't done those either but might fit the bill.
There must be places in Indonesia, French Polynesia, Maldives where you could put together a great resort and diving - unfortunately I haven't gotten around that yet myself either.
