Just a couple of points. When teaching single action with a DA revolver, we tell the students to cock with the support hand while maintaining a consistent and unshifting grip with the strong hand.

My wife had a similar complaint about the base of her thumb being battering by a Kahr 9mm. Problem solved when she shifted her strong hand as far up on the grip as possible. You sound like an experienced shooter so this is probably not your problem. As others have noted, a .38 Special in a Model 10 shouldn't be uncomfortable to shoot.