Get the mediums AND the Contoured Large. You will find using them both is a good idea.
The mediums are great for 'pulling' the tissue outwards, the CL is great for 'expanding' the base & shape of your breasts.
You can start with mediums, then add the CL eventually to end your sessions with, until you no longer need the mediums.
Especially if you're a smaller starting point, you'll really enjoy getting to the point where you can start a session with your mediums, and finish it off with your Larges at the end.
You won't want to use the Larges at first, but eventually you'll be big enough to work with them both until you either reach your desired size or get the XL ones.
I recommend buying BOTH Mediums & Contoured Large. Don't avoid the mediums , they're still a great warm up when you're using your larges.
I hope this helped!!