If there's a second-hand section, this sounds like heaven and I want to work and live there.
(I don't buy new clothes with the exception of underwear and socks, I'm poor, full of eco-anxiety about the fashion industry, and I find thrift store employees to be less judgmental and/or have less fucks to give than retail clothing staff)
I've been thinking for a while that it would've been really cool if there were clothing stores where there were no defined "Men" and "Women sections", as sort of a way to defy the gender binary. And if someone tried to ask the store's staff "Is this for men or for women?" they would respond something like "I dunno, it's probably unisex, you use it if you want to".
Doubt you will find many trans in one particular location to warrant a store. And enough clothing in those uncommon sizes to put on your shelves.
Also, are measurements not just based upon the amount of centimetres that go around your body parts? Why would there be 2 different measurements for men and women?
Clothing measurements aren't even consistent between countries, there's effectively no standard. If where you live measurements are based on something sensible, that's pretty lucky.
The XS/S/M/L/XL sizes of course differ for men vs women, and EU sizes which to me have always seemed like an arbitrary number do too. But usually individual clothing manufacturers provide precise measurements to translate into the generic sizes, because of course that's not consistent either. It's a complete shitshow, but ultimately gender size conversions aren't going to help you with the manufacturer differences anyway. But those really should be more easily available inside clothing stores
Then open it? The problem with capitalism is that is has to be profitable to exist, so unfortunately the likely reason it doesn't exist is because it wouldn't be profitable. To have all those items, variations and services, it would end up being very expensive.
Way back when, a fellow perv and I imagined a clothier called Benders which would have not only gender-specific garments in non-specific sizes and colors but also kid clothes in adult sizes. This was before the alphabet revolution of the late 2010 - early 2020s when we'd look to create enby styles.
Every once in a while we'd encounter a line of clothes that seemed to push gender-crossing / obfuscating envelopes. But no ongoing lines of couture yet.