I love mine, just like you I have a bad back, several plates of metal and wood screws (that is what they look like) hold me together. I also have a nero stimulator under the skin to "shock" my nerves to confuse them and make it stop hurting.
When I bought mine I was the one doing the mowing, I did it on an old Ford 8n with a 5' finish mower. I could stand up on it if need be and use my knees as shocks, some areas I could sit down through.
My "yard" really a field sounds like yours, so darn bumpy, clump grass and mole vole and groundhogs have just made a mess of the place. I can take care of the ground hogs, but I never see the other small critters.
I went with this one:
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Damn expensive but what a time saver and wow does it ever smooth out the bumps. The biggest "mistake" I made is letting the wife try it. She was really afraid of the zero turn at first, she usually did around the house on a regular garden tractor while I did the field. Now I can't pry her off this thing, she actually gets mad when I do mow, she wants to do it.
Now I do around the house, and she does the big part on this monster. I have a small simplicity zero turn with suspension (it is just a re branded Ferris) that I use around the house 42", so it can go in all the tight places this big boy can't really go. We also have a "woods" section that needs done and the big one would never fit between the trees.
Saved my back (when I get to use it) and cut HOURS off the time it takes to mow the entire place.