9MM holsters that fit properly will not fit the .40. Looser holsters made for 9mm will fit excedingly tight. One of the best custom holster makers that still has production type prices is Mark Garrity. You have to be patient though, as he's a full time cop.
I have his Changeling holster, among others. It's an inside the wasteband holster, and has adjustable cant through a fairly wide range. Unlike the Bianchi holster of 20 years ago that was adjustable, this one does not have a gear that takes up a lot of space. Mark's design is ingenius and simple. The quality of his holsters is amongst the best on the planet, and absolutely without equal in this price range.
I have tried Galco, Desantis, Don Hume, Safariland, FIST, and many others. The absolute finest holster that I have ever owned was made by Milt Sparks. There is a wait, but the finished product is well worth it IMO.
As for the issue with fit, I have cured many snug holsters by placing my gun into 2 or 3 plastic shopping bags, wetting the offending holster in a bucket of water, inserting the bagged gun, then letting it dry for a couple of days.