I have got a crumpler backpack to keep my camera and lens' in whilst walking, the problem is it doesn't have a hip strap and the weight pulls on my shoulder inflaming a injury. Just wondered if hip straps would help and if there is anywhere you can get them from??!!

Hip straps would definately help but you can't just fit them to your bag, you would need a bag with them built in to get the full benefit.

A simple foam mat, cut to fit the backpanel, will help to 'firm up' the pack.