In the states we call them mats or floor mats. Most of what you will find is carpeted, though there are some reproduction ones out there. Those look to be universal parts store mats
If you ordered mats from the factory you only got the fronts and had to order the rear from the dealer. I ordered my car with mats and here are pictures of the originals. I have found one set of Red ones on ebay and never another set. They do also sell the rubber Mustang mats that were a dealer option also.
I posted in the past the dealer accessory brochure but here it is again. This is for 73.
When most people see the mats in the pictures they think aftermarket but they do have the Ford part numbers on the back.