I'm 5ft and 120ish lb and I wear a b cup.
I ordered a size M and it fits perfectly, the cup area fits me well and doesn't reveal anything if I bend over.
The straps are adjustable and the item looks exactly like the pictures.
The only thing I would recommend is making sure you wear the right bra and underwear other than that it's a beautiful dress and if you've been wanting one I recommend you get it :)