Another ball-jointed doll I am considering is an Iplehouse Silvia. I like that she is also available in a "dreaming" head sculpt. What I would do is order her body (an SD-size) with the dreaming head, and then also add a regular smokey-eyed Silvia head in addition. I'd be sure to match the color, of course. And then, I would be able to take fun photo shoots of her sleeping and waking up.
These dolls appear to have fantastic bodies, as well--they seem to be able to pose and move quite well, at least according to the photos on the website.
I think she looks different enough from Sky that she'd be a fun addition, but proportionally, she looks more like a real person, and not so anime. I wonder if I could pose her with Sky together, or if she'd look out of place?
Photos courtesy Iplehouse.