Conventional mesh floors are a cause of heat loss(done the experiments and simulations). How much in which configuration/circumstances is a complex question. It comes up regularly at talks and Elaine gives me the evil eye if I look as though I'm disappearing down this vast rat hole.
There's some thing in Bee World this quarter about this topic but its not that informative
I don't see any amount of insulation in the floor keeping varroa in check.