Hi Tracey -
I bought a Baby Gear backpack nappy bag and find that it works very well! It manages to contain the many items I need for DS (and in the early days I carried a minimum of 6 nappies and 4 changes of clothes because of his frequent poos) plus I carry my wallet, digital camera, hat, sunnies, bottle of water, magazine, etc. Good luck finding something that will work well for you...