OP, I use Milt Sparks holsters. I'd highly recommend you look into them before you make a decision. Their VM2 IWB holster is so good I own three. In fact, if I carry it, it's likely in a Milt Sparks. His quality vs. price is unparalleled in the industry. Now I got all mine made from horsehide. I haven't done a damn thing but use them since I got 'em. Still work like new, pistols won't fall out on their own like others that get worn, yet it somehow "breaks in" and feels better over time. Hard to explain. My oldest one is about 10, yet it looks and feels like it's almost new, yet "broken in" somehow.
But if you get a great hoslter, Milt Sparks, Mitch Rosen, etc., there won't be much you can do to them. Cowhide is treated to be on par with horsehide these days, so both are waterproof, both are tough and both are rigid (though I do feel horsehide is more rigid, hence why I prefer the holster itself to be made from horsehide, loops and shit from cowhide).
Make sure you get a good "gun belt" not a walmart belt. Even a cheapo Galco gun belt will do the job, I even have one. It's not as nice as my double thick gun belt I had made, nor the one Milt Sparks sells, but it makes a BIG difference in carry, that belt does.
At the end of the day, I don't think you wanna soften gun leather anyway. You could maybe polish it, but I don't know, I'd ask the maker if that's okay (I can't see it not being okay). The whole point of it is that it's rigid --a solid place to store the weapon and a solid belt to keep everything where it's supposed to be. Of course the leather itself needs to be tough to begin with, hence why I recommend you contact Milt Sparks. Galco makes a lot of mass produced leather for industry, and it's okay I guess, they have a lot of selection, but for my money, I go with the guys that make 'em by hand. I haven't been too impressed with Galco's latest offerings, and I've also had problems with their gear in the past (M9 pistols in their shoulder holsters). Their leather is quite a bit softer than what I'm used to these days. Too soft in fact; some of their holsters can't be reholstered due to the fact they are so soft they fold when inserting the weapon. That's just a no-go.
Good luck, lots of choices, but I'd hold out and get a good maker and wait on 'em... Get a decent kydex for in the meantime (or use what you have if it works). But stiffness in the right areas and proper stitching are attributes to look for in gun leather.