Looking for the right cup

The unfortunate arrival of my period has come after a lovely 14 month hiatus from being pregnant and breastfeeding my daughter. I now remember the many reasons why I dislike tampons and the unreliability of pads. Before becoming pregnant, I started using Instead cups to see if I would like the idea of them before investing in a reusable product. I did really like them, but since giving birth vaginally, they no longer fit properly. They just keep migrating out, causing massive leaks.

I am a mother of 2 children, the first delivered via c-section and the second vaginally. I always thought I had a high cervix, because I can not seem to find it. However, since giving birth vaginally, things have definitely changed and it seems I cannot get a tampon or instead deep enough. They just stop before being inserted completely.

My flow is relatively heavy for the first three days, then regular for about another two, and it slowly tapers of from there for another few days.

I am unsure of which cup to start with and would be very grateful for any suggestions.