I second the suggestion of asking this at menstrual_cups.
But in my personally opinion i'm not sure a cup would work for you. Does it really really hurt you to pull out a fully soaked OB tampon?? (since i know how much they can expand horizontally) Because if so i really think a cup might hurt for you too use. But definitely ask this question in the cup community, plus take a look at all their tags and what not, they have loads of helpful information specifically about menstrual cups.