TBH, I considered some transformer paper soaked with some oil, but I haven't done any testing to see if this would transfer enough heat and be electrically isolated.
My mosfets are not gonna get extreamly hot or dissipate much power. There will be large peaks but its in very short durations under a second or two so even a marginal thermal conduction to a good heat sink would be acceptable.
Whats the best search term to use when looking for sheets like this?
I find tons of other mica things, like capacitors, tiles, you name it.