|I had problems with the contoured waistbands of slacks being too curved. I'm fairly straight. Using this technique I found out my front waist was quite flat but my back waist very curved. My right hip is even curvier than my left hip.
In your undergarments, lightly wrap a piece of very thin interfacing around your abdomen. You could also use tissue paper, or even toilet paper I would guess.
I started wrapping around my waist with masking tape, about 1" wide. Heck, it doesn't matter exactly, this isn't a duct tape dummy, just a mold of your waistline.
Don't make it too tight or too loose, but seriously an inch more or less isn't what determines the "shape" of your waist.
Give yourself about 3-4" of height. Determine where you want the top of your waistband to sit, put a piece of elastic around your waist (have it level) and then mark the top of the waistband. Make marks for the CF, CB, and sides.
Cut it off right at the center front.
Now it's fun to take your tape measure, check the full waist size, check if the sides are close. They won't be exact. If there isn't a major discrepancy just average it out and you have your waistband.
If there is a big discrepancy you might consider making separate pieces for the left or right waistband sections.
I then drew in the top of the waistband, smoothing out the curves a bit, drew it 2" thick, then traced my waistband and added the seam allowances or front closure spaces based on the pattern piece I was copying.
You can use this as a two piece waistband, or 4 piece waistband, or 3 piece if you choose. Just use it with the original pattern piece (for shape and style) but now it fits you.