Layering helps--I think most of us do it whenever we can. I was super-paranoid about my bumps after a little while, so I wound up double binding. Then I wore a not-too-tight t-shirt over the binder, and an open button-down shirt over that.
I wasn't small-chested, but I was in my forties by then, and I had some, uh, droopage. They were still pretty dense, but they hung lower than they used to. So they didn't really mash, but I could tuck them down reasonably well, if you know what I mean. I looked pretty good.
I was lucky because I had top surgery after only a few months of binding. I don't think I would have been too comfortable in the summer with two binders and two shirts.