I have a wrap sweater that I love, that I usually wear over a leotard, or stretchy cami top.
Pinning it looked a little awkward, but a small vintage brooch looks cute.
Another option is to wear a pretty bra that has some color (or black), and put your small, pretty vintage brooch on the part that shows. That way, it looks like a decorative cami, but you don't have to fool with an extra layer of clothing.
Plus, that brooch can anchor the sweater to the bra, so you don't show more than you intended to!