Carrying a 4" K-frame, such as my S&W Model 19, is easy and comfortable. I use a Milt Sparks PMK or 200AW holster, and a nice, purpose-built belt, made by Milt Sparks, Kramer, or The Wilderness, the latter being nylon. A Ruger Speed Six, in the same rig, is equally comfortable.
Carrying a Ruger GP100, or S&W L- or N-frame, is still reasonably comfortable, but the weight will be felt sooner during a long day of carrying.
Obviously, I have to wear more than just a tight T-shirt as a cover garment.
I have also used some IWB holsters that are no longer in production.
Barrel length is NOT a hindrance to comfort! All else being equal, a longer barrel acts like a keel on
a sailboat, making the whole rig more stable. I have also experienced short barrels tending to poke me in a certain spot on the gluteus, when carried IWB, whereas a similar weapon with a longer barrel will bridge over that spot, and lay flat. This is largely a matter of where one wears the weapon.