This may not be practical because of where you live, but hiking has been fantastic for fitness for me.
I have a prolapsed disc in my back and ankle niggles/ knee ache due to a car crash when I was 18
The uneven ground and hills of hiking really help sort these niggles out. It is also great for muscle tone and fitness.
Eliptical trainers and gym equipment is such a repetitive motion, they cause my ankle and knee problems.
Plus hiking is much more fun. And Free (minus travel to the hills etc)