One thing I always have to say on these threads is make sure if you're losing in your band or your cups. There's a big difference there and as you lose weight it's very, very common to lose in your band first so it'll make your cups fit poorly but in reality your band got smaller and you just need to go down in the band.
The way you can fit yourself is make sure you have the right band size first, otherwise the cups size won't fit correctly. The best starting point is taking underbust=band size and then going up in the cups until the center gore fits flat against your sternum, your breast tissue is fully enclosed in the cups and you don't get any quadraboob. To check your band size you should be able to comfortably fit two fingers behind the back of your band but not your entire hand, so it should be tight. I have a guide some help on my blog that you can see
here.
If you don't believe me on the difference a tight band can make check out
his blog.