I have bought a cheapish self inflating mattress from Anaconda. About $100. Looks ok and pumps up to 3.8cm. I tested it on the floor of my garage and seems more comfortable than I would have expected. Not brilliant, mind you.
Having said all that, I am a pretty heavy guy (114kg) and sleep on my side. This puts a lot of force onto narrow areas of the mattress. I have been car camping a lot, and I know from experience that most of the cold comes up through the floor. I camp in Queensland (around Brisbane) so not that cold - no snow or anything, but still pretty cold. So this area is of major concern to me.
I had not really given foam mats a thought - thinking they were an outdated technology. But they might be a good idea to supplement the self inflating mattress. I understand that I should only look at closed cell foam, but that is as far as my knowledge goes. My gut feeling is to go as thick as I can, but most seem to be 6-10mm. I have also seen some with an aluminum layer on one side. That also seems a good idea for insulation purposes. These seem to go for around $30 or so and weigh 0.35kg)
And then there are the dearer specialist items. Like the Thermarest RidgeRest Solar Sleeping Mat (0.74 kg), which is a silver looking mat that is in a hatch sort of arrangement. They seem pretty nice from the pictures. $80 or so.
http://www.cascadedesigns.com/therm-a-rest/mattresses/camp-and-comfort/ridge-rest-solar/productThere is also the Klymit Inertia X Frame, which is a 0.3kg blowup mat with holes all over it. In fact, there is only mate in certain body areas.It seems you can put it inside the sleeping bag, which seems a top idea. About $70.
https://www.klymit.com/inertia-x-frame.htmlI have read of down filled mattresses, but have not actually seen any.
There are also the general inflatable mattresses that I did not even look at when I bought my unit. They seemed pretty big and not for hikers. I could be wrong.
Does anyone have any comments on all this stuff? My first impression was to go with a simple EVA foam mat for $30 or so, but I like the idea (if it works) of the aluminum coating on one side. Or even one of the dearer options if that is the best way to go.