Can you take out the carpet? If so, you can put #3 grommets in the carpet and attach the floor mats to the carpet with plastic Christmas tree fasteners. You can get them in different colors and if you can't find some that go with your floor mats, you can dye the Christmas tree fasteners with SEM products. This is how I attached floor mats to the carpet in an Opel GT.
If you don't like this idea, there are other options.
No one lives forever, the trick is creating something that will.