I enjoyed "Open: Love, Sex and Life in an Open Marriage" by Jenny Block. It is written memoir style, about the process of a couple's experiences opening their relationships.
I don't know if you or your partner is having emotional issues around accepting polyamory, but I did in the beginning. I was very threatened by "The Ethical Slut", because, as Mono put it, I didn't-WANT-to open up. I wanted to understand my HB better, and find out for myself if I could cope with an open relationship for his sake, or if I needed a monogamous relationship, so that we could decide where we were going, and whether it would be together or not. "Open:" was non-threatening, and allowed me to see the struggles of this couple, and also their positive outcome... it was still a challenging read emotionally, but I came away with a sense that it wasn't all about fucking, and that not everyone is magically *fine* with it right away.