The 20cc is minimal, go bigger. If your going under the muscle you will lose some volume, so bear that in mind.
I had 215cc, was told i was 10cm bwd. Post op 1month i felt i was too small. A 32d/dd but look a full B/c at best. I went to another consult who advised im 12cm and 400 mentor wouldve given me the fullness i had desired. Now im stuck as i paid £5k for blites that im not happy with and still wearing a padded bra!