I also have issues with things staying in place. There are a lot of tutorials on how to tuck. I’ve tried the homemade gaff. It was basically the waist band cut off a pair of my guy underwear slipped through a piece of tube sock. I was amazed how nicely packaged everything stayed. When I saw how flat and smooth I looked I was in Pink Fog heaven. (Wow there is a use for guy underwear). Unfortunately, the loops in the gaff created some extremely unsightly panty lines which were probably visible from space. I’ve thought about buying a gaff but haven’t pulled the trigger on one yet. Some girls have found a pair of Spanx or tight pantyhose holds everything in place.
Have fun and remember if you feel pain stop.