I'm currently doing my PPL(H) with Aeromega at Cambridge and am really impressed so far. Small but friendly and high-quality team of instructors and currently 2 R44's, although I believe only one is available for SFH.
One of the Aeromega instructors has an excellent website for PPL(H) students whch I'd really recommend:
www.helitutor.com.
I wouldn't be too concerned about the 'size' of Cambridge. In around 35 hours of flying from there I think I've only seen maybe 15 aircraft movements other than the flying schools. Plus you have full ATC who are used to students and PPLs and generally very helpful.