If you google chair rentals form your departure port, you will find the help you need. One thing to remember, don't leave it outside your cabin. The odds of it being "borrowed" by someone are high.
Depending on the ports you visit, just know some of the curbing is very high,and some streets are cobblestone, which is hard to maneuver over. All the above is worth it though, for the person you are pushing to enjoy the surroundings. Have fun on your cruise.