I know I saw a recommendation on here for a sex education book, but I can't find the thread any more .... DS is now 15, and already has the (excellent) "Let's Talk About Sex" but I think he needs something a bit more "teenage" to cover topics which maybe that book doesn't go into in depth.
"Everything you ever wanted to Know about Willies (and other boys bits)" ...can't remember author. This is a good one because it focuses on boys. When I searched for suitable books for my son I found that most were aimed at girls with a little bit for boys as an afterthought. This covers puberty, sexual health contraception , relationships etc. all from the boys perspective.
Also "Living with a Willy" by Nick Fisher. Similar to above but written in a pseudo blokey style.