I have found these clip and they work great with and floor mat.

Mat-Loc Clips | GGBailey

 

These same exact "Mat-Loc" clips came with a new Mercedes i purchased a couple of years ago and they worked great (maybe the dealer threw them in with the mats). They reminded me a lot of those little clippy things that snapped on the end of my jacket sleeves to keep me from losing my mittons.

 

Well I bought 2 sets and used two clips per mat, keeps them in place but easy to remove the mats for cleaning.