Remember a true "air mattress", i.e. just an inflatable plastic shell, provides nearly no insulation under your sleeping bag. I recommend a foam filled air mattress like the Thermarest or one of it's knockoffs. They can be reasonably light and roll up small but do provide some insulation. Non-inflatable foam sleeping pads can be light and do insulate well but aren't the first choice for comfort.
Actually, that's not quite true. Some air mattresses also have a high R-value. They are pricey, but Thermarest, for example, makes their NeoAir XTherm insulated air mattress (R 5.6). But it is still super lightweight and packs down to nothing.
But I agree that, generally, you have to pay attention to air mattresses when it comes to ground insulation.
A regular air mattress that is just a hollow shell has a very poor R-value. Any air mattress with a useful R-value has some sort of foam filling.
Not true. The NeoAir XTherm is an inflatable mattress (no foam) with an R-value of 5.6, which is higher than closed-cell foam pads. I own one and have used it extensively, including sub-zero temps in the Canadian Rockies in spring and fall, and my first-hand experience has confirmed that these work as advertised.
Here is a link:
https://www.thermarest.com/mattresses/neoair-xtherm-1More warmth per gram than any other air mattress in the world.Exped and other companies also make down-filled air mattresses. You do not need a foam mattress for warmth.
