I know it is an old thread, but I am also wondering the same. My search just brought me to just one downtown store - Mexican Thread and Yarn Company near the Garment District (425 So. Los Angeles Street, LA), but how much I understand they sell just synthetic fiber yarn. The other one is mentioned Moskatel, that sells Michaels yarns.
Thank you for the answer! So layering(that bra is made of two layers anyway)and boning is the answer. Well, it doesn't have to be cotton, but I would like it to be natural and preferably, organic. For health reasons. I am not so worried about sweating and getting cold much.
I like Champion 6242 style bra(it does have underwire and back hooks), but it is made from synthetics, and I thought I would like to sew one with organic cotton or organic cotton/hemp. I could forego the hooks(and make it pull on style), but I think it would be nice to keep underwire-not sure if pull on is possible with underwire.Do I take my Champion apart(or use pins to transfer parts on paper) and just copy parts on the cotton? It probably will behave differently than original fabric. Any ideas?