(((Rozied)))
I think sending him books is a great idea. I would do like you siaid..call the prison, see how much tennis shoes are and send him exactly that amount. The prison my best friend was in would only allow gifts from "outside" at Christmas, and then they had a detailed list of what was allowed. Contraband IS a big problem, so they're very cautious.
Do what you feel most comfortable doing....that's all that counts, okay?
Hugs and prayers!
Amy