"waist (at the navel)" ... "top buckle to be at my navel"

Guys, your natural waist is what we should be discussing---not your navel. Now, it's probably within an inch of the navel, so you should be close. Step one, find your waist.

Mike, if you order a hand-made kilt then (drum roll) you should discuss the measurements in detail with your kiltmaker. That's an advantage of a hand-made kilt, it's definitely going to be made to fit your body and not some Platonic ideal concept of a body. Don't make assumptions from some generalization that I give you, although I hope my generalizations may be helpful! Ask the kiltmaker.