https://www.kmart.co.nz/product/office-chair-mat-with-grip-43025329/     I got a mat from KMART,  its thick and mine has little spikes on one side to keep it in place on carpet.

I take it outside on the driveway and pour warm water on it to smooth it out every so often if a corner folds up leaning against desk leg or similar ,  then just leave it to dry so its nice and flat,  when it cools its perfect again.  ( recommend doing this when you first get it as they come rolled up ).

Cheap and they last,  Ive had mine a few years now,  also have one under the cat litter robot to protect carpet.