I'm not a backpack user - as I'm a wheelchair user, I chest carry my setup using Lowepro products.
The kind of setup you describe, Ellen, is relatively compact. It's almost certainly smaller and lighter than my setup (EOS 20D, BG-E2 grip, EF 24-70mm f/2.8L, EF 70-200mm f/2.8L IS and, when it turns up in the mail today, Speedlite 580EX), especially if you're not carrying lens hoods. Most backpacks will be on the large side for your equipment, and that will just exacerbate the problem of getting something to fit when you're relatively short and slight.
One thought that comes to mind is what I'm considering for my setup. At the moment, I'm using a Toploader 75AW, carried on the included chest harness, which isn't great. The other bits are sliplocked to the Toploader.
I'm considering moving the whole lot onto a Lowepro shoulder harness and deluxe waistbelt - more musings about this setup can be found in the dialogue in this thread. I nearly ordered the Lowepro harness and belt this time round, but I've spent up for this month and I may need the flash next weekend.
In that thread, you can see cjtinkle's Lowepro vest harness and deluxe waistbelt setup - though you may find the shoulder harness a better bet, as it's available in four different sizes. You have various options for what you put on the harness and waistbelt - you have the flexibility to use different lens cases and so on, or you may prefer to stick your whole setup in a Lowepro bag that's compatible with the harness.
A Lowepro Specialist 85AW
may be ideal - that bag includes a waistbelt, so you just need to add the shoulder harness if you want the harness. Several of the pictures on the Lowepro page linked show the bag with a shoulder harness on it.
This isn't going to be the cheapest option, but it should be flexible and adjustable.
David