An illustration of women's underpinnings from a 1910 catalog in my collection. Note in particular the "mono-bosom" brassieres in the upper left and right corners. My favorite, though, is the nursing corset just below the brassiere on the upper right. See how the little flaps unsnap for breasteeding?

Here's a great 1912 corset ad from a catalog. Note the corset on the lower left for nursing moms. Flaps unsnap to provide access for breastfeeding. These corsets are extremely rare and valuable now.