Brain Lock https://www.amazon.com/dp/006256143X/ref=cm_sw_em_r_mt_dp_U_LPRxDbDVXJK65 by Jeff Schwartz is a really good book on OCD and a 4-step process to help. We read it later on in the process of dealing with my OCD and it confirmed some of the things that we realized were helping.
Back in Control https://www.amazon.com/dp/0988272997/ref=cm_sw_em_r_mt_dp_U_SRRxDbFZAZVA2 by David Hanscom MD. This book was written by one of the top back surgeons in the world. He talks about the connection of stress in life and mental/physical issues.
Feeling Good https://www.amazon.com/dp/0380810336/ref=cm_sw_em_r_mt_dp_U_zSRxDbYSKKPGJ by David Burns is a book that is basically about Cognitive Behavioral Therapy for mental illness and OCD. I haven't read this one, but Matt recommended it.
And lastly, one of Matt's favorites, The Body Keeps the Score, https://www.amazon.com/dp/0143127748/ref=cm_sw_em_r_mt_dp_U_rTRxDbBY7ETD4 by Bessel Van Der Kolk. It discusses the connection of trauma and suffering to mental and physical illnesses and how our emotions, thoughts, stress affect our physical body. I've heard him refer this book to tons of people!