I agree with the splits suggested by slohairt for the measurements that you've given.

You might want to consider adding 1/2" tp both the waist and hip measurements before you do the splits, though, so that you have room to change size. You'd put the buckles and straps on at the actual measurements but make the kilt 1/2" too big. That would make the splits

waist: 21 1/2 (apron), 20 (pleats) (or 21 1/4 and 20 1/4)

hips: 22 14 (apron); 22 14 (pleats)

I'm really concerned about the length. How tall are you, where does the bottom of your Gordon kilt fall on your knee, and how many inches is it from the top buckle on the Gordon kilt to the top edge of the kilt?