I've tried 3 methods: 1) my regular NeoAir, kinda like Mike M does, 2) a stiff 3/8" pad rolled up with gear stuffed inside, and 3) the same pad folded with it against my back and gear against that.
I like the NeoAir best...by a long shot. I place it in the pack paying no attn to air, stuff my gear in, then inflate the NeoAir a little (I leave the valve up top of course).
With the 3/8" pad rolled with gear inside....I feel like I'm carrying a barrel on my back that wants to roll side to side. I felt like the 3rd method put the weight of my gear to far from me...and it seemed uncomfortably stiff.
I'm using a small pack (ZimmerBuilt Zen) and carry between 7.25 and 10 lbs, total....with no hip belt. I also do what Randy Martin does: stuff clothes and sleeping bag inside the pack sans stuff sacks.
I feel similarly to Mike W too. For me, I don't think anything is needed, really. But, as I said before, of the 3 methods, I much prefer the NeoAir. It's soft and conforms perfectly to my back. As a plus, I get to sleep on it at night!