Possibly not relevant to an RV, but if you can work one in, I would try using a recliner chair. I have had the extreme back problems since my 50s. I found my best method of sleep and healing was by using a recliner chair with chair arms. You position the chair settings the way you like it and sleep in the most ergonomic position possible, which is on your back.
All your appendages have good unrestricted blood flow and being on your back doesn't restrict your breathing like it does when laying on your side. There is absolutely no need or desire to twist and turn at night in your sleep and aggravating your back injury further. The arms of recliner stop you from turning and twisting in the night and further injuring your back. Best of luck, I understand your wife's pain.