Best heel height for a bad back

Most folks with bad backs say they must wear flats. I find my back feels better with a heel height of about 1-1/2 inches. If I wear a totally flat shoe or boot, I feel as though I have to hold myself forward, which puts a strain on my back. Of course I cannot and do not wear high heels ever.

I have back pain the length of my entire spine due to osteoporosis. The chronic pain is mostly in my upper back, lower pain happens with strain. Don't know if that makes a difference.