dogs, welcome to iRV2.
If you're looking to buy a new motorhome, there are some manufacturers who will alter their designs to suit the needs of those who are handicapped. I think one of them is Winnebago.
That being said, I don't know if they would be able to significantly alter the design of the entry steps because most manufacturers use pre-engineered steps designed and built by others. I don't know if anything is available to suit your needs.
There are, however, supplemental steps
available that you can set on the ground to help make that last step less of a hazard. There are also auxiliary handrails available that might help make the climb easier. These handrails extend quite a ways out from the body of the coach to give you something to hang on to while climbing, and they fold flat for travel. This link
shows an example of the handrail, but I have seen designs that extend out even farther.