Dude, don't limit yourself to Yellowstone proper. If you want some amazing camping in the area go up to the Beartooths 15 miles outside the northeast entrance to the park. like Lower Aero Lake and out to the Sky Top Lakes. If you get lucky with the snowfall level there is a route up Granite Peak (highpoint of Montana) that's nontechnical if you go in the late summer and have a little luck with the weather. Though it's really dangerous if you get unlucky and this one shaded area is icy. There is also supposed to be a great 40 mile one way trail, I can't remember the name. But you won't have to deal with Yellowstone crowds.
Or hit up Yosemite-Ansel Adams Wilderness if you haven't done any backpacking there. One thing I absolutely love about Yosemite is there is no assigned backcountry camping. You just stay where the you want as long as you're not within a couple of miles of a road and not within a couple hundred feet of water. No hanging your food, you just bring a bear canister that's also a nice chair when you're cooking or eating. You don't schedule so if you're feeling lazy one day or really want to bust ass and cover some miles, or maybe just want to spend the whole day exploring one area you can do it. Who wants a schedule when on vacation? I agree on backcountry sleeping, nothing like when it's 25 degrees outside and you have sleeping bag unzipped to let some of that cool in. Just stay away from Half Dome, overrated as and the crowds suck. Plus Yosemite has about the calmest weather you'll find above 10,000 feet (the Beartooths definitely don't though). Just make sure to properly acclimatize if you're doing a trip with some real elevation.