Made from
The Margot pyjamas come from Tilly and the Buttons first book Love at First Stitch. The pattern is for a woven but these are made in a fairly heavy, monstera-print knit (also bought from TATB).
The piping and waist tie are made from a remnant from my stash. The piping cord is cotton yarn.
Construction
I added a separate waistband to these because I prefer the shape and fit. I removed the top of the pattern piece where it folds over and added seam allowance.

The holes for the waist tie are made using the stretch buttonhole on my machine.
The tie is a just double folded and top-stitched.
I also stitched in the ditch at the side seams to hold the elastic in place and keep the gathers mostly to the back.

I also lengthened the legs by adding cuffs to the bottom. I added seam allowance to the bottom of the leg piece and cut out cuffs double the length of the finished cuffs plus seam allowance. Then I added piping at the seam between the leg and cuff to match the waist tie.

Of course, there are also in-seam pockets because…pockets.

Pretty much everything was sewn on the overlocker.
Verdict
Properly comfortable and my favourite pj bottoms by a considerable margin.