Look into getting the latest Fodor's Cruise guidebook. It has the most up-to-date info on cruising and accessibility of the current ships.
Here are a couple of other sites to check out as well:
(look in the disabled cruisers forum there)
If you are not very experienced in travel with a disability, you might be more comfortable on your first cruise working with a travel agent who specializes in this. Once you get some experience, you can often work with any travel agent who can learn your needs and work with you on finding the right cruise for you.
Here are some travel agents who specialize in this:
You also need to consider that you will be responsible for all his care, including transfers (beds are lower than beds at home), all personal care, and getting around ashore. You might want to look into traveling with a PCA or younger family member who can help out. I travel with my parents on cruises as my mother has MS (quadriplegia) and my father, although healthy, is 80 and unable to do any lifting anymore. Finding cabins that sleep 3 and are wheelchair accessible is a challenge. Sometimes I have my own cabin next door and find a roommate to go with me. We also take with us a mobile travel lift that makes transfers much safer and easy on the ship. The one we have is here:
Unfortunately you are not going to find senior discounts, and many discounted prices you see advertised do not include the fully accessible cabins. Accessible cabins tend to go very early during booking, so it is best to book as far ahead as possible. A good travel agent will be able to help you with this. Be aware that you can often find bargin prices in the summer or fall for the Caribbean, but this is also because this is the hurricaine season and you risk at least a change in itinerary if not cancellation of the entire cruise if this should occur.
You might want to try a short cruise round-trip cruise out of LA or San Diego first (Mexican Riviera, for example). This would allow you to focus on the cruise without also having all the hassle of fluing to/from your cruise ship.