At 22, I was diagnosed with rectocele, stage 1 uterine prolapse, and cystocele. (http://www.pfdnetwork.org/what/index.html) During my period, the least amount of straining, even to pee, would push tampons out - painful, because dry tampons hurt. So I started using the small Diva Cup because it was easy to take out every time I needed to pee, removing it often didn't irritate anything, and I wasn't throwing away so much trash! I really liked the cup. It didn't bother me even that it sat very low since my cervix was only about 1" from the outside of my body during my period.
Last December, I had surgery to repair all these pelvic floor problems. I had a hysteropexy, where they reconstruct the uterosacral ligaments from a synthetic mesh, and another layer of mesh was layered between my vaginal wall and my rectum. It's nice to have everything in its place, but my vagina is a lot tighter and more rigid, I guess, since the surgery - I mean, there's tight mesh behind it! So the Diva wasn't working for me because it angled back toward the posterior mesh and pushed on it - it was achy and painful. I've been using tampons for a few months but really missed using my cup. So I just bought a small LadyCup, and it seems good. Still a little achy, but since it's very short and soft, it puts MUCH less pressure on the rigid mesh areas. Cutting the stem off seemed to really help the minor pain, too. I'm not too concerned about the small volume this cup holds because I'm used to removing my cup every time I go to the bathroom, anyway, and I wear cloth reusable pads too on heavy days.
So, if you've had these surgeries, small/soft cups seem to work! And if you're considering the surgery and need input, I have plenty to say about it :P