Protect it from what? My seats are never covered. I would not want them covered because one feature I use almost daily is the ventilated seats. Covering them would defeat this feature. I use a hammock in the back seat periodically when I bring my dog along so that she cannot slobber and drool all over the place or make a mess when she is feeding on snacks while in transit. I should note that my car seats are black. When I was in the showroom I recall seeing one model with literally white seats... I remember thinking, why would anyone buy this? Sure it looks good right now, but in a matter of weeks the seats will look soiled. Simply entering and exiting the car while wearing blue jeans would discolor the seats in no time never mind spills and other mishaps.
I don't get why you need covers too unless you have those crystal white seats However, my friends order custom seat covers from this site - carid.com/2016-mercedes-gle-class-seat-covers, there are a lot of different styles and colors, you can also choose what material you want whether it's cloth, leather etc.
I've only ever sat on seat cushions in cars and that was when I as a kid in my mom's car. It was just so odd and uncomfortable IMO, something over an ergonomically designed seat.
If dirt and such is a concern, there's always the option of detailing you car's interior once in a while to keep it clean.