I don't have a direct answer for you. All I can offer are some observations that perhaps will help in your search and in contributing to the discussion. I like these types of holsters for the reasons Chief38 mentioned. They really are thin and easy to conceal.
From what I'm reading, Bell Charter Oak used a clip that was/is very effective in holding to the waistline fabric of the pants or shorts. My experience with a few of the classic rough out holsters is that not all will hold fast to all clothing. It is sobering to do a bunch of draw or draw and dry fire excercises and have the holster stay with the revolver even once. Then try to figure out why it happens some times and not others and if anything can be done ot correct it.
The clips on some (many) are bright finished or have other features that can attract the eye if not covered. Some were intended for narrow belts, others for wider pants belts, and some are pretty snug and do seem to work clipped on the waistband under the belt.
Another characteristic that varies a lot is placement of the clip relative to the cylinder and the trigger. This positioning makes a big difference on whether the gun will tilt forward changing the cant, as well as whether the butt rotates away from the body or toward when worn in various postions around the waistline. Without a belt, and on lightweight garment, this is going to be even more pronounced.
Be very interested in what you find. perhaps the seperate belt under the shorts will be a better solution?
This is a 1970s Buchemier Clark Model 61 for a 2" J with a 1.75" belt clip.
Same model from 1980 or 81 which was used AIWB but note that cant is forward and probably intended for 3-4 o'clock carry.
Don Hume H715 size 3-2

Although it looks similar, it is slightly smaller overall, a little wider at the bottom, more vertical cant, and fits the gun and the pants differently than the B-C model 61.
Personally for AIWB, I think a clip further forward would better keep the butt rotated in. In the summer this can be an issue - at least with me.
Final note. These do not retain the pistol when laying down.