I'm looking at some clothing for fall for R and I'm not sure which size to order. She is currently 22.5 pounds and 31.5" tall at 13 months old.

12-18 months is 22-27 pounds but 29"-31"
18-24 months is 27-30 pounds but 31"-33"

I'm thinking about ordering some dresses in size 12-18 months and just adding leggings underneath if necessary. I'm worried that 18-24 months will be huge, weight-wise. Thoughts?