Your question deserves more input than who makes the best pack. 1st of course is your weight in line with your height? Can your strengthen your lower back and stomach muscles with: leg lifts, side bends, crunches, etc. There are many excersises that can be done at different levels to do this.I would consult your Ortho doc about this.
I would also consider getting the best boots you can afford with arch supports. There is information here for that also. As far as packs...Badlands makes great hunting packs or you can go with the upscale/lighweight backpacking packs like REI sells. There are a of discussions here about packs you can get answers to this question but strengthening, stretching are going to be as important as the best pack. Happy Hunting, Matt