The question of religious dress is complicated, especially if you don’t live in a cloister. As I said before, it should be practical. It should fit with my values. But “practical” includes “can wear it without it becoming the center of attention”. What often happens when I wear a salwaar kameez to work is that people’s brains stop short at my clothes and they don’t hear anything I say that doesn’t involve the word “India”. As a minister it’s not all about me. But my clothes can make it all about me, which is bad if my goal is to get folks thinking deeply about religion or something.

So okay, it should blend in. What’s out there already?

Of course we have to consider the all-purpose robe. With the right cincture (belt) it might even blend in.
Knowing how practical the salwaar kameez is, that goes on the list of models.
The sari has that infinite-size-changing quality, as does the sarong, and in pants, the dhoti.
Lots of women committed to subtle plain dress are choosing jumpers.
I have to say, overalls are pretty comfy, and I’ve seen some professional-looking ones.
There’s also a thing called “fat pants” or “thai fisherman’s pants“–a kind of stitched wrap pant–and ordinary wrap pants.
For warmth we have the usual: jackets and sweaters, leggings and tights. I’m not dealing with overcoats, socks, or underwear–that’s a whole other headache.

So just in major indoor clothing we have:
1) six yards of undraped fabric
2) robes
3) tunics
4) baggy pants
5) skirt
6) pants or skirt with bib front
7) jackets
8 ) sweaters
9) wrap-around clothing: pants, skirts
10) vests

That’s a good selection of options to start. Really, only shirts are missing. Perhaps a pirate/renaissance shirt? Of what we have, robes, tunics, baggy pants, jumpers, overalls, and wrap clothing can be inherently size-flexible.

To make others size-flexible you’d have to add something subtle: elegant lacing, adjustable buttons, something.
To make them sustainably produced they’d have to be of organic fabrics, sewn probably by one’s self or in a cottage-industry model, preferably fairly locally.
Then to make them affordable, you’d need to have the option of mixing and matching your entire wardrobe–maybe a palette of tans, whites, and blacks to start–so that you only needed maybe 20 garments for a whole three or four season wardrobe. That would also help reduce the overconsumption that tends to come with seventeen different reds in one closet. (Now you need seventeen of any red accessory…)
With natural and unique fabrics I can’t imagine how to make the red from one dye lot match another, so incorporating color would be tricky.

Of course, there’s always a simpler way. One of my rural colleagues has taken to wearing black Carhartts for work. It’s tempting.