I agree with HSKR R/T, ditch the liner, they don't protect your bed, they actually harm it. A spray in liner will not only protect the bed but will also prevent items from slipping around the bed. I just purchased my 2020 Ram 1500, and it had a slip in liner in it, before I bought it I made them take it out so I could check for possible rust where liners can get grit in between the liner and bed sanding down and exposing bare metal to moisture. The bed did have scuffed areas, but no rust. My opinion, and it is an opinion, not to spend any money on bed protection, spray in a liner after you used the bed enough to scratch it up enough to warrant the cost.
Back to a custom fit mat, I made one for my wife's 2001 Tacoma because I couldn't find a nice enough fit and quality mat. I used to work with fabricating and vulcanizing conveyor belts. I custom fit it by making templets out of cereal boxes and sheet metal then cut it to fit. I realize most owners don't have that ability, so the easiest is to have a spray in liner done, it'll look better and do what you need.