I have an interesting idea for a market for you to consider, based on my experience.

So some people move through sizes, in a shockingly fast period of time. After I saw a reddit text post I had to google 5'6" 196 pounds since I have trouble picturing different heights and weights and couldn't follow them along, I got as a result a self-post showing a large size change over a relatively short period[1] -- notice that just 13 months are between the first and second-to-last picture; that's nothing! Also it seems thousands of people encourage each other along such journeys, both men and women, which is presumably why they posted it.)

Okay now on to the reason I'm writing this comment. I've known this is possible and suggested that an overweight friend work out and stick with it, and she did. But check this out, I hadn't considered something. After just a couple of months she didn't own a stitch of clothing she could wear anymore. (she was too fit for the clothes she had owned.) She needed to buy new clothes.

So what are people supposed to do if they start exercising hard for a few months, if they had long been over-weight and simply don't own any intermediate sizes? Especially if they're continuing to steadily move down in size? I would think borrowing attractive clothes that are your current size would be a good solution.
It's like the opposite version of a hand-me-down! :) There are thousands of people doing this and supporting each other. One thing though is that there's no reason this would be limited to women, your current approach is very gendered.
Borrowing cute clothes in any size is a great thing to do for someone moving through a size but not for that long. Buying new clothes every few months must suck. Just a thought!

[1] I've moved these two a footnote: this self-post https://imgur.com/a/XdFW9#uQXfAu6 [this shows someone who posted stats in their underwear], for equality here is a male similar example https://www.google.com/search?q=196+male+5%276"&tbm=isch - this is not about people's bodies but changes in dress sizes, and I had only just searched for height and weight.

EDIT:
Another thought. Someone in this thread mentioned apprehension over meeting someone - but if you were meeting someone because they're now too fit for the size you want to borrow from them, that would be a great reason to meet them as you could very briefly discuss exactly how they did it. I'm male and if I were trying to really bulk up (become very muscular) and borrowing designer clothes from someone whose biceps were too big for their old shirt (bear with me) that would be a reason to meet them I imagine.

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EDIT2: I'm getting downvotes, even though I had a friend complain that she needed new clothing. If this isn't a market based on the above, where am I going wrong?
Lots of people start gaining weight and outgrowing all their clothing or start losing weight and becoming too small for all their clothing. Perhaps I should add that nobody is responsible for their weight, nobody has any obligation to change it, and also possibly genetics mean that some people cannot move up or down in weight by any extent over any appreciable period of time.

This comment is just about a market that I've heard complaints from, where there is a natural need for temporary clothing. . . I've also seen my friends selling old clothes on facebook based on their former sizes. . . .