I look for second hand leather straps at pawn shops and garage sales...and usually just toss the guitar. I've found the aged straps to be denser due to the free range donor's exposure to the elements and coarser wild forage. Very important when accessorizing an otherwise non-descript instrument.
I've tried strap modelers but none of them really give the strap in the room experience. I mean come on. They're just trying to emulate the real thing! It will NEVER be as good. Digital straps are just toys for the iPhone generation. Next year, they'll say "this time for sure!", but I say, "that trick never works!"