Good morning James and all! James congratulations! I am preparing for the same exam. I purchased "The CMQ/OE" book. Did that also help? Or do you suggest any other materials?
There are a couple books that are referred to in the question bank that I own. They are the "Quality Toolbox" (excellent book) and "Juran's Quality Handbook". They are useful, but not necessary for the test.
Lastly, lean on your experience and knowledge. That is the most valuable thing. Good luck with your exam!