For cardio, how about rowing? It might be hard on your back, but if you're doing squats it might be OK. Or swimming, or biking.
For upper body, I'd say go ahead with the wall pushups. Did you get some physical therapy exercises? You could use the machines in the gym to continue those also. You should also incorporate an upper body "pull" like lat pulldowns or cable rows. Or if you prefer bodyweight exercies, you can do inverted rows: Inverted Row