A scooter would be even better to use on the ship. It's hard to push a wheelchair over miles and miles of carpeting. It's even harder to push yourself in a wheelchair over carpeting. A folding wheelchair would be best for taking off of the ship, for shore excursions, as they can be folded and put in the trunk of a taxi or in the luggage bays of a bus.
You can rent either or both of the above at home and take them with you, or you can rent from CareVacations.com or Scootaround.com, and they will have them in your cabin waiting for you when you arrive for your cruise, and you leave them in your cabin when you get off the ship. Very easy. If you DO decide to rent/purchase at home, the airlines carry wheelchairs and scooters as luggage, at no cost to you. You can even ride them to the gate, check them there, and have them delivered to the gate at your destination.
If you have trouble walking distances at all, I would definitely have some chair or scooter ready to use when you get tired. Scooters give you more independence, but chairs are less cumbersome. You would have to have a cabin with a door wide enough to admit a scooter, or a folding wheelchair if you do not have a handicapped cabin.
Have a great cruise!