I like just the
Addison spelling. It doesn't sound delicate or anything, but I still quite like it for a girl. It just doesn't sound right for a guy in my mind.
There aren't really any middle names I'd like if it were a boy's name, but if it were a girl, I'd probably go with something more regal and feminine to balance the name out, like
Clarisse,
Teresa, or
Elise, or something more cute, like
Bo,
Scout, or
Zoe.