What type of firearm do you want to carry? There are many styles, leathers/fabrics, brands($$$ types).
In general you will want a shoulder holster that fits your torso-chest & is adjustable but w/o a lot of buckles, snaps, ridges, sharp edges or cheap elastic.
I prefer the angled horizontal type like the slick Aker Comfort Flex or the high end Kirkpatrick Leather style. Gravity is your friend,
. The slanted angle offers a secure fit but a smooth, even draw.
For hot weather or humid climates I'd suggest a natural leather or maybe a light brown. Dark or black leather may bleed or stain your clothes.
Consider your off-side carry items too. It will balance the firearm weight & be more even. Spare magazines or speed strips(revolver), white lights(tactical flashlights), OC spray, knives, etc can all be added in some shoulder rigs(depending on the brand).
Some good sources to check include; Aker, Galco(the Miami Classic II), Mitch Rosen, Ken Null, Bianchi Intl, LawmanLeather Goods, Del Fatti, Mernickle, Don Hume, Blade-tech, Kramer Gun Leather, Kirkpatrick Gunleather, El Paso Saddlery, DeSantis, Alessi, Gould & Goodrich, Unkle Mikes/Michaels of OR.
Contact the holster maker or custom shop first. Wait time or products may be delayed. Exotic leathers(bull, horse, rhino, shark, etc are available but you may wait longer).