I use this https://www.amazon.com/dp/B07R1MV14F/ref=redir_mobile_desktop?_encoding=UTF8&psc=1&ref_=yo_ii_img to protect the entire rear bench, and it works great. Also have the seat back covers linked by cns0329 above, and the all weather mats from tesmanian.

The seat cover does not effect the safety of the car seat. As long as you attach the car seat properly and secure the belts and straps all the way down so that the top of the car seat doesn't budge by more than an inch, you are fine.