@pockets I got around the issue by using a heated mattress pad. It consumes 13w on the lowest setting and meant that I only need one blanket (fleece material). Dog approved.

I put 1" of XPS in most places, 2" of polyiso on the celiing, and 0.5" of polyiso at the head and feet of my east-west bed platform to ensure enough space. All the insulation was bought used or overstock from construction sites. Craigslist was my friend in the endeavor.