This is a nice quality dress. It runs true to size according to reviews (does not run generous). If in between sizes smaller of the two would be more vintage length and if you want regular/added length go with larger size.
Blakely is 32 pounds and 35 inches modeling a 2T in the Spring Jewel (dark navy stripe chest).
In the Floral Equestrian (horse floral print) Vivian is 27 lbs and 37” wearing a size 2T.
Karringten is 45.6lbs and 45” tall wearing a size 6 (in the Botannical Blooms turquoise & mint floral dress).
In another dress with similar style: Size 8 47" 50# perfect fit