Many things you can use to insulate a tank: poster boards (the kind with foam center, in black or white, @ Walmart+ other stores carry w/ school supplies)
are easy to cut & tape on, or corrugated cardboard, or even self-stick carpet tiles. Styrofoam (in sheets) is great but messy to cut...you can use cork (sold in
rolls) too, even packing-bubble sheets (incl. the kind with foil outside, aka "hot water heater blanket"). To make it look nicer, I like to first install nice scenery
on the back & sides of tanks, then the insulation, so you only see the scenery. But there's nothing wrong with the plain poster- or card- board etc either.
Actual blankets would be awkward.

What a lucky snake, that you're making him so welcome. I fear he's been neglected, poor soul. (I'm in AR, not close neighbors, darn it!)