Making A Warmer Truck Camper Bed

I'm south of Medford Oregon tonight. It's 35 outside. My mattress insulation project seems to be working but, I'm turned around in bed, feet forward by the front window, head at the foot of the bed. My head is comfortably warmer now and my feet don't mind the cold. Furnace on for 60 degrees but the cabover bed area has much greater exposed surface area to i ternal volume than the rest of the camper and as such, is susceptible to much greater and faster temperature swings. The extra blanket is doing the trick.