Apparently it's been established that I breathe through osmosis, as that conversation actually took place when I was cosplaying last weekend, but for other people I believe it just takes getting used to. You should practice binding your chest while you're just sitting around at home and it's easy to go adjust it if you need to. It takes some practice to figure out how tight you should do it to make sure that you're flat without actually being in pain. What you should use for binding partially depends on how much you need to bind. If you're a smaller cup size like me, then you can probably get away with just wearing a sports bra, wrapping an ACE bandage around it, and safety pinning the bandage in place.