Hellobee Boards

They're not recommended as they could compromise the safety of the seat (crash tests are not performed with any accessories). We have leather seats also but chose to forego the protectors.

ETA: so far our seats have been fine without one.

You can use a piece of non slip drawer liner. Actual seat protectors aren't supposed to be used because most interfere with the seat, britax tests their brand of seat protesters with their seats but they're the only brand i'm aware of that does. There are going to be car seats covering those sets for the next 8 or so years, I wouldn't worry too much about whether the car seats leave dents in the leather. My leather seats have always gotten dents from car seats, doesn't bother me.