I have a MaxMate Premium Tri-Fold Truck Bed Tonneau Cover 2002-2018 Dodge Ram:
https://www.amazon.com/gp/product/B00REJXVEW/ref=s9_acsd_hps_bw_c_x_1_w

I've had it about a year and a half and it still looks great. It was a low priced option (about $200) Consider adding a tailgate lock if you don't already have one.