Hi Rita!
Here is a great page on the Disney website for info:
Guests with Mobility Disabilities. Disney is committed to making your visit as carefree and convenient as possible, so read this page to learn some practical information on navigating Walt Disney World.
In addition, you will earn that wheelchair and Electric Convenience Vehicles (ECV's) are also available for rental at the Parks on a first come, first serve basis, if this is something you would like to consider.
Two of the Parks are quite large, and require lots more walking than the other two. These are the Animal Kingdom and EPCOT. They are so amazing, so I would hate for you to miss out on the opportunity to see them. You may want to consider using your "walking days" for the Magic Kingdom and Hollywood Studios, which are a bit more compact in their design. Then, if you choose, rent one of the wheelchairs or ECV's on the days you visit the other two parks.
As for places to stay, you will find that each of the Disney Resorts provide excellent transportation to and from the Parks via the Disney Transportation System. This includes buses, boats, & monorail! They will conveniently transport you from your Resort bus stop to the Main Entrance area of each Park, so where you stay will not make that great of a difference in your walking.
Some resorts are larger than others, so when you make your reservation, you may want to request that you be located as close as possibly to the Main Lobby area and conveniently beside a bus stop. This request cannot be guaranteed, but they will do all they can to accommodate you. Also, make sure you remind them of this desire when you check in.
I hope you have a wonderful time in Walt Disney World!