I use mashed up cooked yolks, sweet pickle relish, and Miracle Whip.
DMIL uses dry mustard in her recipe, and always made them until about 24 or 25 years ago when MiddleDD was about 5 or 6. At a family dinner, MIL asked her if she wanted an egg. She said, "No thank you. I like Mommy's better." I have been the egg maker since then.