Finding the right cup!

Assia • 22💖Mommy to 2 fur babies🐆❤ piercing/tattoo enthusiast😊

Hey ladies, recently I've been considering switching from pads to the cup! I took the quiz thing and the Lena sensitive came up. My question is, how do I determine if I should get the small or large? Or both? I have a heavy flow, all days of my period. Any advise/suggestions would be appreciated! Thank you💖