The challenge....

Recreate this adorable outfit! How cute is this? I am in love with every aspect of it! The seller that has this on Etsy, however, wants $115.00 for it. A bit pricey. I want to make something similar for my niece, Claire for her birthday in October. The problem. I got no pattern. The solution??? Modify an existing pattern or draft my own using a sloper. Modifying a pattern is something I have done to a small degree in the past, but this will require a lot more than I have done before. I have never worked with slopers before, but I am considering it for this project. I checked a book out of the library the other day that gives me instructions as to how to make them, BUT, I don't have Claire here to measure, as she lives in Texas, and I am in Minnesota. I could maybe get Carrie (her mom) to do it for me, I don't know. I am relishing the chance to really draft my own pattern, something I have wanted to be able to do for years, but never had the guts to really try it, but I am scared that it won't turn out right, especially with no one to try it on and see how the fit is. I really need a child size dress form. Should I do it?