The Back Sufferers Bible
Sarah Key
This book has been widely used by my clients over the years.  Sarah Key is an  Australian Phyiotherapist who practiced in London and also treated the Prince of
Wales, the forward in most of her books is written by HRH. 

Sarah clearly exlpains several of the most common back
complaints and what treatment is available and also how to treat yourself.  The major benefit of her books is giving you the knowledge that pain when exercising does not necessarily mean more harm. 
Other books written by Sarah Key include Keep Your Joints Young, and Back In Action

Body Control Pilates Back Book
Lynne Robinson, Helge  Fisher and Paul Massey
A simple and effect guide  with an  explanation about  back pain and exercises specifically designed to  target your
back muscles to  strengthen and support you. I have found this book very easy to  use. For each  exercise it tell what it will do and it encourages you to master each level  before moving to the next.