It's difficult to know what procedure might work best for you without seeing photos. But there certainly are options for you. Sometimes a lower body lift is done to remove loose skin from the lower back and upper buttocks and lift the buttocks. If you need more volume, fat...
I have seen a couple of patients who have had Thread Lifts for the buttocks as well as the thighs and even for a tummy tuck. I think that they have been used to try to lift just about every part of the body. They may work in some situations, but I can't speak from experience as I have never...
Congratulations on your weight loss. Unfortunately I don't think there is anything you can do surgically or non-surgically to resolve the laxity. Working out in the gym while wonderful to do won't fix it either because it is not possible to hypertrophy muscles enough to take up this lax skin.