| If you find that thread loops tend to tangle, pull out and twist too much, here's a suggestion for an alternative. You have to plan ahead, because these have to be added during construction:
Take two long strands of elastic thread together, using a piece of solvy (not necessary, but easier) under them, thread through the hole in your presser foot (use a cording foot if you have one), and set a zig-zag to just cover each side. Don't make the zig-zag too dense, as you want them to stretch to cover the button. (rinse off solvy if used-and dry)
Insert the loops, measured and cut to fit over button when slightly stretched, with tails to seam allowance, in between your construction seams as you finish garment opening.Use your button placement marks to mark the opposite side for placement.
I usually go over the area with the loops with a very small stitch to help prevent them from pulling out. I also stitch over them twice.