I know just the thing you want, just not sure they make it anymore.
Back when I used to work hardware/lumber we sold an asbestos board intended
to be used underneath of and behind a wood stove.
I forget what we called the thing but I wouldn't be surprised if it was
"stove board" as has already been suggested.
Check a place that sells wood stoves. There must be something equivalent
these days. People are still needing to put wood stoves on floors.

ml