I’ve been using a Mooncup for four years since by twins were born - it’s been absolutely brilliant, reliable, cheap and totally reduced period pain.
What follows will definitely contain TMI about my fanjo. Sorry about that, avert your eyes if squeamish.
This month, however, it keeps slipping down and, um, chafing. There’s no stem on it, it’s the end of the cup rubbing against my labia. It was absolutely awful. 
I think things are starting to move south and my cervix feels a lot lower, and as such, the mooncup (size B) is too long for my poor post-partum vagina. I’m absolutely sure I’ve got it in right.
Anyone got suggestions of an alternative? I’ve googled quite a lot and I can’t find specific measurements. Thanks in advance! 