Google "Belly Band Zack", it's a retrofit of a standard Galco underwraps.I have one that I use when I need really deep concealment. I find the part where the velcro meets to be uncomfortable if I don't have a T-shirt underneath it--but then the pistol is supposed to be comforting, not comfortable. The other downside is that it's a collapsable holster. Having said that, it does an excellent of holding a small pistol tight and hidden, without any tell-tale clips etc. I think it's superior to similar options like "thunderwear", since it holds the pistol tightly in place and allows a better grip before drawing.
Google what I said, may not be exact, but it's probably close! Nothing new, nothing groundbreaking, bu it's probably been thought of! If you have the Jack for a patent, go for it!They don't really protect the trigger if they're just stretchy material. I wouldn't carry with a round chambered in a regular belly band because you can easily pull the trigger through the fabric. The Crossbreed version didn't end up working well for me - it protects the trigger but was too floppy and bulky. The Can Can holster works well as far as holding a small gun well, and they have a men's version of it (I have only tried the women's).
I have an awesome idea for a belly band holster that would protect the trigger really well, maintain the low profile and comfort of a belly band, and allow you to easily swap kydex shells, I'd love to get it made.
Google what I said, may not be exact, but it's probably close! Nothing new, nothing groundbreaking, bu it's probably been thought of! If you have the Jack for a patent, go for it!