|My favorite pants and skirt patterns have no waistband, just a faced waist with darts that sits slightly below the natural waistline. But my waistline and tummy size seems to fluctuate, so sometimes the waist feels too tight and sometimes it will slip and slide.
My Goldilocks solution for a "just right" fit is this: add elastic! I use a soft, wide knit elastic that can withstand stitching. My preference is 1". Wider would probably work even better, but is not available locally.
1. After the back and front facing pieces are stay stitched and seamed together, I mark off the seam lines on the short ends which will eventually be attached to the zipper opening.
2. I cut a piece of elastic about an inch smaller than my best (smallest) waist measure. It will be stitched to a facing and garment cut to my largest possible waist size.
3. Working on the wrong side of the facing, pin the raw ends of the elastic against the marked seamlines on the short edges of the facing. Align the long end of the elastic against the waistline seam. Accurate staystiching will be a good guide for this. Secure the elastic with pins in 2-3 places such as side seams or center back/front, evenly stretching the elastic between the pins.
4. Using a lingerie stretch stitch or long zig zag, stitch the elastic to the facing, close to the waistline edge of the elastic. It is important to leave the bottom half to 2/3 of the elastic unstitched so that it will be able to stretch out more than the waist edge of the elastic to accomodate the curve of the high hip.
5. Pin the facing to the waistline of the garment, right sides together. Stitch, being careful NOT to catch the elastic in your stitches.
6. Grade and trim the seam allowance as usual. Turn the facing to the inside and fold back the facing edges next to the zipper. I like to topstitch through all layers instead of just understitching the facing.
7. Secure the lower edge of the facing as usual with vertical "stitch in the ditch" or hand sewing at the sides and center front or back.
Note: I know that I read about adding elastic to a waistband here on PR and in sewing resource books, but I can't recall seeing anything about elastic in faced waistlines. Since I've bought a pair of RTW pants with a similar treatment, I'm sure there is a published tip for it. So I do not claim to have an original thought here.