A small hijack Sorrel and co, for the greater good so I'm sure you won't mind 
A few words about differing cup sizes and how to manage them
You do not necessarily have to pad the smaller cup to balance the bra out. I'm about a cup and a half different and never use fillets. The trick is to choose styles that can disguise it. The hardest style tends to be balconettes IME.
To balance the smaller side, hoick the smaller breast towards the top and centre of the cup, as if trying to pull it towards a pendant on your necklace. In many cases, the material at the bottom of the cup will gather/pucker allowing the breast to sit on it, thus filling the top of the cup like the fuller side. The empty part of the cup is now at the bottom and so will not show once you are dressed.
Cleo Juna and many half cup styles are often good for such disguise. They're also great for loss of volume post weight loss/breastfeeding.
Tshirt styles that work include Freya Deco (it gapes but lays flat once clothed) and the Panache Porcelain.
Fuller cup styles are good, particularly Panache Andorra and Melody full cup, and the Fantasie side support styles such as Elodie.
Nearly every woman I fit has an obvious size difference but in 5 years, I can count on one hand how many times I've needed to suggest adding a filler of any kind.
Back to you 