Husband is my doula

⚡️LaLuna • My beautiful rainbow baby arrived on her due date! Baby girl born on 7/2/16. :)
So my husband and I are planning on him acting as my "doula" during labor/birth. We are planning an all natural birth in a hospital's birth center. I was wondering if you ladies had any good recommendations for a book I could get for my man to read to help prep him/us for this. I've already read Ina Mays childbirth and breastfeeding books so I've got that covered. And we are NOT hiring a doula so please don't just suggest that. I'm looking for helpful resources for my husband. Thanks!! :D