If you were in Iceland I would probably tell you to get a Land Rower or a Nissan Patrol on 44-48 inch tires
An EVO or an Impreza would probably work for you. Those back problems are horrible. I am having some backproblems that come and go but not allways so bad I have to lie for a few days. I don't know how the seats are in those cars but it's really important to find a car with a some comfortable seats