These discs are perfect. They are harder than rubber or silicone so they don't squish down.
These are not 320mm in diameter. If you read the small print it says that but the title says 320mm. Better read all the fine print.
They do what they are meant to do- protect the porcelain floor. They stick well, just make sure to give it a minute after putting them on before moving to around.
At least the adhesive backing is worthless on smooth surfaces. Black felt from this outfit sheds a lot of tiny black fibers.