It seems like a lot of top women are already entered into the women's doubles, so perhaps it'll be a lady who's only entered into singles or only doubles. Having said that, maybe a player may be willing to forego women's doubles to play with Andy. How often do players play all 3 events unless they're expecting to lose early in singles?
I think he needs an accomplished singles player who has also won plenty of doubles - best bet being someone who is also in form. I'd probably say someone like Garcia or Azarenka who can hold their own and not be seen as a weak target. I know he has had good things to say about both in the past, and he lost the Olympics mixed final vs Azarenka, so that'd make sense. Andy also has a lot of fun during practice, so probably someone a bit jokey would link up well.