Hi Lisa,
Not to worry - Disney is a great place to visit for guests who require many types of special assistance
There aren't that many rides that utilize conveyors belts in the boarding areas.
Off the top of my head, at the Magic Kingdom Peter Pan's Flight, Haunted Mansion, Buzz Lightyear's Space Ranger Spin and the PeopleMover all utilize the moving walkways when boarding. Space Mountain, the PeopleMover and Pirates of the Caribbean have conveyor belts when exiting. Space Mountain and Pirates of the Caribbean have alternate exits. At Epcot, Spaceship Earth and The Living Seas with Nemo have conveyor belts.
Some of these attractions do have alternate entrances while others do not. See a Cast Member at the entrance of these attractions. If you have problems safety transferring while the conveyor belt is in motion, they can briefly stop it to allow you to board.
Check the link on the Guests with Disabilities section on the WDW website for
Guests with Mobility Disabilities. There you'll find a list of the attractions for all four of the theme parks which allow Guests in ECVs to remain in them, which attractions require guests to transfer from an ECV to a wheelchair to board (there will be courtesy wheelchairs at these attractions), which attractions allow guests in wheelchairs to remain in them and which attractions require Guests to be able to transfer from wheelchairs to board.
Please keep in mind that Cast Members are not allowed to lift Guests on and off of attractions.
Wishing you many magical memories.