I use these very soft silicone ones that up me by about 1.5 cup size. Currently I'm half way between B and C cup so approx. a D cup with these in. The positive is that wearing these has confirmed that D will be way too small on my frame. I really need DD or E to be where I would like after augmentation. My Care bears dress is size 18 to fit my shoulders and rib cage, but the breast material just flops down over even with the boosters in. The problem is 16/18 UK dresses assume large breasts so are impossible for me to fill. But I cant go smaller unless I get shoulder and rib surgery!
They are comfortable though, I don't even notice them there to be honest. Pop in my bra over my own and they stay. Just means I can wear t-shirts now and not look flat chested, as my own boobs are invisible in anything that doesn't cling skin tight! Also its a way I can get used to my size after augmentation as I'll only be having slightly bigger inside me. The only thing missing is a cleavage, so there is no option to show the upper part of my breasts. Always got to be in a fully covering bra, so definitely looking forward to when that's finally an option.