There's girls fit that description, they've been well reviewed on here and they will all be linked from the PuntingWiki links above.
Trouble is the popular girls are already likely to be well booked in advance for tomorrow unless you get a cancellation.
I'm thinking the likes of Brooke Knights, Honey Rose/BlondBabe Honey, Teen Jade or Lily Delphine. Might have more luck with an agency girl especially one that's got positive reviews but hasn't hit top in the popularity stakes and is therefore always booked.
Antonia of Diamonds is off as she's Polish and probably too popular, but have a look at Frankie May (not sure how gym fit she is) or Zara at Diamonds, Cheryl of Amour or some of the newer indies like Ava Rose or maybe the more established Jade Heart (37 but toned).
Sure others could come up better ideas.