Someone else wants this? Cool! I thought I was just weird.

For the "eeighted blanket with no heat retention" I've played around with the idea of creating a metal mesh (high heat conductivity) woven into a large piece of fabric. You'd probably want the mesh covered, but if it was fine enough it could be covered by just a thin layer of fabric and still (I'm hoping) feel fairly comfortable. That would be an "anti-blanket" in that it would help you radiate heat instead of storing it. At least in theory :-}.