For my GP100, 4”, 6 shot, I purchased a Gould & Goodrich holster. Excellent craftsmanship. Don’t think I’d ever carry conceal though unless I had a trench coat or was going for a woods walk
P.S. My only holster advice that is any good is don't cheap out. I remember someone getting an unlined leather holster that had rust forming on a single action revolver in a matter of days. A quality leather holster will NOT do this.
I have a Simply Rugged Pancake holster for my S&W M66 2.5" barrel. I really like the way this holster holds the gun "high & tight" also the quality seems very good.