Sorry to hear about your back, wish you all the best. There's some good avice here already regarding medical options and second opinions. FWIW I feel that I benefit massively today from a contested decision not to have surgery on my lower back some 5-6 years ago.
I'm going to suggest that you do lot's of test riding too, feel what works for your back will be the main thing. A few ideas that come to mind:
- I'd stay away from minimal suspension snappy race-day designs but instead go with a designer that is a leader in fully active magic carpet rides.
- The magic carpet desings work best with proper platform dampers to get a responsive ride. And in my book the daddy of all platform dampers is the Curnutt as used by Brent FOES. Check em out, awesome bikes.
- But really, think out of the box, and I've said it before on this forum: for a sore back go 29er.
The bigger wheels and lower pressures offer very real benefits in the ride. they make for a distinct plus in comfort and the front end is nice and high by default. And now plenty options are availabe including proper full sussers. I've been on a Lenz leviathan 29er with 3" rear travel for 5 months now and it is the best XC bike I've owned. Plus it feels as smooth as my 5" Foes FXR, but faster. And I rode it up and down some nice technical stuff in the Harz in Germany no problems at all.
Take care