When I used a self-inflating pad, I used a 3/4; I discovered that my Granite Gear Vapor Trail had an open-cell back pad as part of the suspension, so I just put it end-to-end with the self-inflator, simultaneously giving me a full-length pad and solving the problem of where to store the pack.

When air mattresses came along (again, much improved), they were thicker than the pack, and as a side sleeper, the "drop" hit me right at the knees, putting too much sideways pressure on them to let me sleep comfortably. At that point, I went to a full length pad and a very light frame pack, and stored the pack on its edge inside the tent or inside the vestibule (depending on how much room was in the particular tent and what the critter risks were. I woke one night to find a raccoon dragging my niece's pack from her tent vestibule toward the treeline.) The lighter pack and full-length air mattress was still lighter than the Vapor Trail and short self-inflating pad. And, like you, food always gets hung in a tree - we don't have real bears, but we do have "mini-bears" like mice, squirrels, and raccoons.