I used to work at an outdoor retail store which rented equipment. We would rent out massive down bags rated to minus 40, and the guy (it was always a guy) would complain that he slept cold, and he wanted his money back.
“Did you use a sleeping pad?” I would ask innocently.
“No, I left it home to save weight.” Ha! No refund.
The pad is not only for comfort, it is for warmth. The pad protects your bod from the cold, hard ground.
Foam pads are warm, but they tend to be heavy. Open cell foam pads are bulky, and they can absorb water. Closed cell foam pads are light and cheap, but not the most comfortable.
Air mattresses are comfortable, but tend to be heavy. There are new backpacking mattresses out there which are expensive and light. They are fairly durable, but if a hole does present itself, it can make for an uncomfortable couple of nights. Carrying a patch kit is advisable, but finding the leak can take a chunk out of the day. Cheap vinyl mattresses from the Dollar Store won’t last through one night, and abandoning same on the trail is NOT advised.
The self-inflating foam/air mattresses have become the industry standard. The thin layer of foam within assists in protecting the bod when the mattress springs a leak. In theory this works, in real life, it is still a ver-ry thin layer of foam.
A full-length mattress is more comfortable, but obiously it is heavy. For warmth, the torso-length is sufficient. Many of the newer pads are cut in an oval rather than a rectangle to save weight.
There are women’s sleeping pads, which tend to be shorter and narrower, because, after all, girls are always smaller than guys, right? But they are pink, which counts for something.