Hello LadyMac72,
My wife and I are avid cruisers and my wife Joanie has been using a moterized wheelchair for a number of years now. I can offer a few suggestions for you and a cautionary not or two as well.
First, the bad news, be careful when booking excursions through the cruise line as the are often not accessible for scooter or wheelchair users. More than once we have booked an excursions that was described as accessible only to be refused inclusion at the dockside. The problem is that the people running the tours have the right to refuse access to those with mobility issues. There is little recourse. Secondly, even if you find a "Accessible excursion" there is very often little or no accommodation for wheelchair/scooter users in the ports. Unfortunately many locations have no infrastructure for accessibility; ie, no ramps, curbs with no curb ramps, no elevators, no way to cross streets. Even gaining access to restaurants and restrooms is often difficult or impossible. Traveling with someone who requires a W/C or scooter dosen't just limit your ability to visit many ports. In some cases it makes it makes it nearly impossible.
Now, the good news. There are a companies out there who specialize in making arrangements for those with mobility issues and can tailor your experience to your needs and abilities. Even things that, until recently, were simply impossible to consider for those like my wife. For example, Joanie and I visited Machu Picchu, Peru last month with the assistance of a company that make the impossible possible.
The bottom line is that you have to do your research and plan ahead. Read about the accessibility of the ports before your arrival. If necessary make arrangements with locals who can assist you with your planning.
Remember that mobility issues may make traveling more difficult but in many cases still possible.
Good luck and safe travels.