Read reviews for the Campbed 3.5 by REI as submitted by your fellow paddlers. All of the reviews are created and written by paddlers like you, so be sure to submit your own review and be part of the community!
I compared the Camped 3.5 to the considerably more expensive Exped SIM 10 Comfort mattress. I preferred the Campbed because there is no tendency to roll off its edges, whereas this is a problem with the SIM. Also, the fabric of the Campbed feels softer against bare skin.
I also compared the Campbed 3.5 to the Exped Synmat 7, which is about the most comfortable backpacking mattress you can buy. The Campbed is noticeably more comfortable, but also a lot heavier and bulkier.
As a kayak camper I normally use the Synmat 7. But if I'm only going a short distance I strap the Campbed to the rear deck because it really is more comfortable.
I'm giving the Campbed 3.5, size regular, a 10 for its category. Understand that there are many car camping mattresses that are more comfortable, but that's a different class.