First of all, congrats on the bra fitting! :)
I don’t know of any ways to make your breasts actually smaller, but a lot of my full busted friends tell me that a good fitting bra (well fitting bra?) makes their breasts look smaller. I’ve even heard some women change their minds about getting a breast reduction once they’ve gotten a better bra (that isn’t a condemnation of breast reductions, of course; rather it’s about encouraging women to explore all of their options).
If you’re looking for bras in your new size, I’d recommend checking out this post - The Top 10 Brands for Full Bust and Plus Size Women. I hope it helps!