I've got 3 regular Racer X straps, a custom order extra wide Racer X, and an extra wide automotive dead stock strap from Couch. All of them are grippy enough on my shoulder that I have no problems with slip, they remind me of the upholstery on a booth in a dinner, where you always have to shimmy a little more than you think you need to getting in. The deadstock one switches to seatbelt material down where it adjusts, and it's become my go to for the guitars that don't have a dedicated strap, as the adjustment is super easy, but the wide padding is enough for the heaviest and/or most neck-dive-y instruments.Those do look great! Do you find them slippery? or do they grip pretty well?
I avoid leather straps because I hate the way they adjust. I always find myself in between two of the available slots, either just too long or just too short. I prefer a continuous adjustment and a fabric with a little grip, seat belt straps and the common nylon ones are too slick.
I've been using a Mono Doolittle for years, and never had any issues. I'm the type that puts a strap on each instrument and never takes it off, though.
I've also been curious about the Reunion Blues Merino Wool and the [Invalid or Expired Link Removed].