As Rich was indicating, the first step to self-protection is a firm belief in the sanctity of your own body, and your inviolate right to be unmolested. (What one of John Wayne's characters described as "being willing.")
As far as the mechanics go, even one with some disability can find a system that uses the body in motion to generate power. If you can walk without undue strain, you can generate all the power you need. A good teacher can help you focus on techniques that will not strain your back.
As Rich further indicated, having a weapon is a great second step after mental conviction to not go quietly. Simple movements usually work best, unless you are one of the few dedicated enough to spend years achieving physical mastery.
If you would like to e-mail me, I would be happy to attempt to locate a good teacher close enough for you to visit.