A book I've owned for years has exercises for the back muscles that you do laying down. It's called 'Oh! My Aching Back' by a Leon Root. It's out of print but available thru Amazon and other places. I've gotten it and given it as gifts for friends w/back issues.
It is a 'period piece' due to the times it was written [discussions on pain-killers are now sort of funny], but it's got good explanations on how your muscles work normally and abnormally when stressed in any way. Why they spasm and all that. The exercises are all pretty passive as you are flat out on your back or stomach doing them.
The illustrations are easy to follow and classic - new books seem to use identical ones.
I don't know if these would be acceptable with your issues LizaJane, but some of these exercises could probably be done and not make your issues worse..providing you get that old doctor OK. Seems sometimes that the more times change, some things remain the same [these exercises for example].
Hope this helps! - j