I have a cheaply one from marshalls that has lasted years.

Something like this though maybe work for you? I looked up “split seat rear cover” so it’s not one piece.

https://www.amazon.com/4Knines-Without-Hammock-Middle-Capable/dp/B00UXWJPIS/ref=mp_s_a_1_5?keywords=Car+Seats+60%2F40+Split&qid=1640809025&sr=8-5