For two months, I read and re-read posts on here. Finally, based on sizing info, and success (and failure) stories with various cups, I purchased a medium MeLuna with the ball. I have plenty of room width-wise, but have a very low cervix, and needed something short, wide, with a firm rim. The medium MeLuna was exactly what I needed.
I usually have the worst time with leaks when I am laying down, and I happened to get sick right before my cycle this month, so I have been spending almost the entire time in bed. Normally this would mean tampon + pad + getting up every few hours to check for leaks. This time, with the cup, I haven't even had to use a backup pad. It has been wonderful.
Thanks again, everyone!