Thanks for all your comments.

Yes, our mats were on a thickish carpet too.

Now I'm thinking of replacing all the flooring so that it doesn't turn
into too much of a mish-mash. We have a bungalow. Carpet in the
hall, study, lounge, sanded floorboards in the bedroom, vinyl wood-
effect planks in the kitchen, vinyl tiles in the bathroom. Having
looked around, its really hard to find anything that would look OK in
all rooms AND stand up to the office chair punishment. As there are
old floorboards everywhere, I'm guessing that a layer of hardboard
would be needed underneath too. Unless these really thick Rhinofloor
type vinyls would work without it?