In the early Eighties, there were plenty of relatively inexpensive IWB holsters, made of thin suede-like leather, with spring-steel clips, that would work with belt-less slacks, more or less well enough that they sold well. The problem was that the leather eventually molded itself to the weapon, so that the holster would start to remain on the weapon, when it was drawn. That prevented access to the trigger guard, until one used his/her support hand to peel the holster from the weapon.
Some few holsters makers have made improved versions of the mass-produced suede IWB holsters, using much stronger metal clips, enabling belt-less carry. I think that Kramer Handgun Leather might still offer such a rig.
Much better-made, among the vintage rigs of the past, was the Bucheimer “Semi Shoulder” holster, worn outside the trousers, with a stronger clip, and a paddle-like portion inside the trousers, which was made of sturdy leather, and carried the weapon somewhat high, so that if worn cross-draw, the ride height was similar to a vertical shoulder rig. I recently found one of these on the evil bay, and when it arrived, I was dismayed to see that the stitching was decaying into what amounted to powder, though the leather remained in decent shape. It was so inexpensive, that I did not ask for a return/refund. Perhaps, someday, I will use it as a model for a project. This serves as a cautionary tale, however, for anyone thinking about ordering vintage leather, with the intention of actually using it.
Really, I am liking the Phlster Enigma, for something that I can wear over the undergarment, but under the outer garment, independent of the waistband of either garment. The Enigma is what I see as the ultimate evolution of the belly band.
As for the historic origin of the belly band, the earliest widely-commercially-successful belly band rig may have been offered by Bianchi, back in the day, but, I have little doubt that smaller operations, or independent tailors, created such rigs, far in the past.