Curvy to us refers to a D cup and above, regardless of underbust size. 

If you are a full 32C or 32D, choose S(Plus). If you are a 32E, choose S(Curvy)

If you are a full 34C or 34D, choose M(Plus). If you are a 34E, choose M(Curvy)

If you are a full 36C or 36D, choose L(Plus). If you are a 36E, choose L(Curvy)

Curvy also refers to a bra size of 38B, 40B and 42B, which correlates to a XL, XXL or a 3XL