Seems like these insulated air mattresses are taking over for cooler weather and winter. My old go-to mattress for winter was a TR Trail Pro. heavy and only moderately warm at R 4.0.
My new “luxury” sleeping mattress is an REI Insulated mummy shape, size Regular.
Weight: 15 oz.
Warmth Rating: R 3.7
With the Sea to Summit 20L. inflation bag (doubles as clothes bag) I now have a mattress that is 1 oz. lighter than my TR Prolite Regular and a lot warmer – good for shoulder seasons down to the upper teens at least.
For winter I’ll add a 3/16 layer of closed cell floor underlayment foam. Amazing stuff and it works at 0 F. with the Trail Pro and an LL Bean -20 F. down bag.
BTW, just noticed the photo again that you are “hot tenting”. That’s brave with a nylon tent. I assume you have an excellent spark arrestor on your vent pipe.