Below 0°C, insulation matters: a mattress with a low R-value loses more heat to the cold floor, even with Camp Mode running. Check the maker's published R-value before a winter trip.
The EXPED MegaMat Auto (R-value 8.1) is the cold-weather pick: it has the highest overall score (7.8) of the mattresses that publish an R-value. The Snuuzu Model Y has the highest overall score of the 19, but Snuuzu's product page lists no R-value, so its insulation cannot be compared on paper. Havnby publishes a higher R-value, 13.9, for its CloudCore, an air bed with a foam top that scores 7.6.
The highest overall score of the mattresses that publish an R-value. Self-inflating foam with an R-value of 8.1, 10 cm thick. A multi-SUV pad rather than a Tesla cut. Out of stock at EXPED USA and REI on 1 Oct.
Comfort foam over a pressurised air layer, 20 cm thick. Snuuzu's product page lists no R-value, so there is no insulation rating to compare with the EXPED. It also has the highest price of the 19, and no sleep trial.
Luno rates it 3-season, with an R-value of 1.5. Pure air, 10 cm thick, in two chambers with a split zip. Ships to the US, Canada, Australia and New Zealand only.