Now we can look at our modern clothing system, at least what I see available here in the US.
We have a system where clothing is made for the mass market, rather than custom commissioned, in assembly line conditions. So far, there's nothing necessarily wrong with this. Assembly lines can create significant efficiencies of labor. However, the working conditions (safety, hours, pay, etc) are all terrible. Independent of that, there are other problems with the clothing being made. Even if I could wave a magic wand and immediately fix all the labor issues with how clothes are made, we would still have work to do.
The clothing is made to be, generally, highly curved (high wastage) and generally very fitted. Even in garments that have significant ease, there are often still measurements that need to be within narrow ranges for it to fit the wearer. It's made for mass markets, so it's made in specific "sizes" that correlate something like a dozen different measurements of the human body. It is wildly unlikely that most people will find garments that correctly match their own body in all of those measurements.
The common refrain to this problem is that you just go get your garments tailored. This is ridiculous.
Firstly, these garments are not made to be tailored. They aren't sewn with the seam allowance that garments intended to be tailored later would be. Consider: new wedding dresses. They are usually sold with unusually large seam allowances in order to allow for them to be let out. That is what a garment intended for later tailoring looks like, and it's a perfectly fine solution for a garment like a wedding dress. (That is: a garment intended for one special occasion rather than regular wear on a changing body.) And this extra seam allowance isn't added in most garments, partially just to save fabric, yes, but also because it adds bulk in a finished garment. If it's not going to be tailored, that makes it less suitable for most people who have no intention of getting their purchases altered.
Secondly, tailoring is a lot of human work. Full tailoring is also expensive, naturally, due to this. Frankly, it's logistically impractical to imagine that it would be affordable for all garments that people practically wear. Especially given that people's sizes change over their lives; garments would either need to be replaced with newly tailored garments semi-often, or the same garments would later need the same tailoring to occur again. Simple tasks like hemming or letting out hems might be quite simple and affordable, but the current design of clothing would potentially necessitate entire rebuilds of the garment for many common types of clothing to fully tailor them to properly fit, especially for people whose shapes vary more from the "standard" shapes designed for. Even if we assume a magical perfect communist future of whatever flavor you like, it would still be ridiculous for full tailoring of every garment to be the standard.
But. Making things fit "properly" only requires that much work due to the specific way we dress.
If we were willing to accept some other tradeoffs, could we have standard sizes that practically worked better for people? What trade offs? What designs?
The current system is built on horrific injustice and cruelty. It's not actually sustainable or workable without those things. We have to minimize the work per garment if we're going to dress justly. How can we do it in a way that's workable and reasonable within our modern expectations?