In Uran's case, it would be cute to see her cosplaying Comet:

The girl from the middle or Nene who is the little girl with the dress.
The boy from the left is Tsuyoshi who is Nene's twin brother.
Also it would be fun to see Uran dressed as Comet Star-Power or Meteo-san:

Meteo-san is the girl with a displeased look at Comet's right.
She could be a bad influence for Uran, specially if she teached the infamous noble woman laugh or tantrums.
Here is another cool option for Uran's cosplay:
Meteo-san alternative winter clotes and Comet-san alternative winter clothes:

You guys could suggest any interesting cosplays for both Atom and Uran too^^
With images, if possible.