I think Fatal Silence by Robert Katz is a really interesting book to read. It doesn't deal as much with Vatican policies as the title or subtitle suggests as there are other topics covered in the book such as Anzio. I found the accounts of Italian resistance fighters and the Ardeatine Massacre to be the most interesting and compelling.
I also read a couple of books about the Italian campaign, and heard it was brutal as hell. Obviously the Italian landscape was perfect for defense so..wonder why did Churchill insist that it as a 'soft' underbelly is beyond me