Try a padded or 'T shirt' bra - gives that extra bit of protection. I don't play the melodeon, but I do carry a giant in a similar sort of harness. Plus the seat belt in the car rubs as well. A lightly padded bra helped enormously.

The leather corset will only work if the boobies are squished down inside, rather than being forced up the neck and pointing Nor-east, Nor-west.

The only real cure is to give up the melodeon.... Oh, I wish!!! : )

LTS - melodeon hater but H&S rep....