In this design by Little Turtle Knits, you decide the yarn and the gauge, and the rest is accomplished with those choices and a few select measurements. It is labelled an "advanced" pattern because of the required measurement and the wee bit of math that is involved prior to the knitting. The actual knitting is very straightforward and easy. So, do not be fearful of the advanced label, if you can add and subtract (and do a bit of multiplication, too) you can do this pattern.
Consider making several, for different seasons or outfits, or making one as a gift for a very special friend. What a way to encourage babywearing and show your love at the same time!
Since this is a you-pick pattern, needle size and yarn requirements will be dependent on your choices of yarn weight and size.