Pretty much any leather holster is going to wear the bluing on the slide to some degree, especially on the front edges.
If you don't want any slide wear, a Crossbreed or similar knock off is the least damaging to the slide, IMO.
In leather holsters, I like Brommeland & Sparks; Brommeland a little better as the leather is thinner & it has a little more cant.
Here's a Brommeland Max Con V with a Dan Wesson Guardian (4.25" barrel).
MM