Dee Zee bed mat. My truck came with a spray-in liner, but no matter what, the Dee Zee mat was always going to go on. Mainly because it prevents anything from moving around you place on it, like boxes, loose tools, whatever, they stay put without having to strap anything down.
They also prevent damage of more fragile stuff you stick in your bed, such as finished wood furniture you don't want a rough spray-liner scratching up. I had only this type of mat on my 2015 F150, which had no other liner, and after 4 years of hard use, the bed looked brand new under the liner. Never once did I clean under it during that time. The sale man thought I never used the bed of my truck.
Dee Zee bed mat (or any similar heavy duty rubber mat), get one!