I am looking for the same thing honestly, and it is the reason I decided to join a bariatric forum!
So, Google says there are a whole bunch of things that help with skin elasticity (the main being collagen), and skin elasticity is the key words when trying to have skin that either stretchs without stretch marks or skin shrinking and going back into place without as much loose skin. Some of the things I have seen listed are collagen, retinal, reinoids, hyaluronic acid, genistein isoflavones, witch hazel extract, cocoa flavanoids, etc... but I have been having a hard time finding a single pill or powder with multiple things (like a multivitamin) and it has been frustrating... and I am absolutely certain I am not the only person who has wanted something like this, and something has got to exist, but I just can't find a good one.
Right now, One of the things I am looking at is this:
https://shop.purityproducts.com/skin-health/ultimate-collagen-formula
A couple of things I like about it is that it does not just contain collagen, but some pre-cursor proteins to help your body to make it's own collagen, and some other things to help absorption and stabilization. And even more so, as a scientist myself, I love the fact that they actually referenced pubmed articles which are actual peer-reviewed scientific work... not just opinion pieces like many fad kinds of products list. Still... although a pretty advanced collagen supplement, it is ONLY collagen, and I really wish I could find something that is not to expensive that is far more comprehensive.
