But no matter how much I exercise the excess skin won't snap back.
Congrats on your weight loss! Unfortunately, we are often left with excess skin that cannot be corrected with diet and exercise. I would recommend a buttock lift where the excess buttock skin would be removed by an incision at the buttock crease. This provides a much smoother and tighter buttock but you will be left with a scar at the crease. Please make sure you have realistic expectations about your final result and have an in office consultation to be properly evaluated.
Congratulations on the weight loss! A buttock implant would look wonderful and really help to fill up that deflated skin. However you may or may not have some residual loose skin. If so it can be removed a few months after the implant has settled. Be sure to choose a Board Certified Plastic Surgeon that specializes in buttock implants and has a extensive experience with such procedures.