First of all - don't bad backs suck? I had back surgery on my L5-S1 a few years ago...
One thing to keep in mind is your ability for you to stay with your BC if ever the two of you become separated. For instance, if for whatever reason your tank slips out of your BC during a dive and you have to take it off to correct the problem. If you are diving in a 7mm wetsuit and your weight is fully integrated into your BC, you are faced with a real challenge. If, instead, you wear some led on a belt and some in your BC, things are a lot better. Personally I like to keep all the weight out of the BC (I dive with a harness and a backplate, but even when I had a Zeagle Tech I put my weight on a belt)
For cold water diving, I dive with the DUI Classic harness (with 400g undergarments, a DUI TLS suit, twin steel 110s, an AL 40 deco and an aluminium backplate I use 12lbs).
For warm water diving I only need 6lbs with a shortie and an AL 80, so I don't bother with the harness.
Definitely recommend the harness. It shifts the weight strain from the hips (and back) to the shoulders.
The other thing I would recommend is that you verify that you need as much lead as you think. I've worked with folks via my job who come in extremely over-weighted but had always dove that way and never really thought about it. It's amazing what proper breathing and finding your true neutral point can do to shed pounds off the waist...
Anyway - hope this helps.
PS - though my back will always be a problem, after the surgery (and many month recovery) I am doing remarkably well, so there's hope...