Cosplaying as misa amane?

If you don't want to make it leathery, then just a plain cotton is fine (that's what mine is made out of). You can buy a petticoat (hot topic or online are easy) and put it underneath, or buy some crinolin and attach it underneath the skirt. Since her's is so simple, buying a black dress and adding to it might not be a bad idea, but it's difficult to find a dress with the same lacing up the front as hers has. Good luck!