The following brands have cute bra & panty sets in large cup sizes. Some use UK cup sizing, some use US cup sizing, so make sure you check which one first:
Playful Promises
Parfait
Freya
Elomi
Panache, and their sub-brands Cleo and Sculptress
I'm a 40FF and usually go down 2-3 cup sizes for camming bras so I can have some cleavage, my correctly-fitting size doesn't look as "sexy" and I often have less traffic when I'm that covered.
Sockdreams.com has lots of thigh-high socks, stockings, and legwarmers, and they wear-test items and give measurements that the items will fit.
For babydolls and other types of lingerie, I wear a solid-colored bra underneath, because let's face it, that cute lacey thing isn't going to support me no matter what I do.
And don't underestimate the sexiness of your everyday clothes! A cardigan over a bra and panties, for example, is a great sexy look on cold days, especially if you add a beanie and thigh-high socks.