A reminder (mostly to myself): the most eco-friendly thing you can do is just wear what you already have. Second best option is to shop secondhand. But if you decide to buy new shiz, here are some good options!
If you like LOFT … try AMOUR VERT
If you like ANTHROPOLOGIE … try SEZANE and BALZAC
If you like MADEWELL … try NISOLO (shoes/accessories) and FRANK AND OAK (clothing)
If you like AMERICAN APPAREL … try UNIVERSAL STANDARD
If you like ANN TAYLOR … try VETTA CAPSULE and MODERN CITIZEN
If you like TALBOT’S … try EILEEN FISHER
If you like J.CREW … try CUYANA and SUMMERSALT
If you like ABERCROMBIE … try MARINE LAYER
If you like SAKS and NORDSTROM … try THE REALREAL
If you like PANDORA … try ANA LUISA
If you like ALTAR’D STATE … try CHRISTY DAWN
If you like ADIDAS … try VEJA
If you like STITCH FIX … try MATERIAL WORLD
If you like to splurge on designer bags … try REBAG
If you like H&M, ZARA, etc., search for those brands on secondhand sites like POSHMARK or THREDUP
*Just a reminder that there is no real definition of what a “sustainable” brand is, and there’s no Sustainability Czar that can tell us who’s doing it right and who’s melting the ice caps. But some companies are certainly trying harder than others. The above are all brands/retailers that I’ve looked into and/or bought from and I am happy to support. But these are all my own opinions and you are certainly free to form your own opinions, which may be different from mine.