GotolyWomen Butt Lifter Shapewear Hi-Waist Panty Double Tummy Control Knickers Waist Trainer Body Shaper

Im a size 16 hip (pandemic weigh) and twin baby weight..will it flatten my baby belly? is an xl going to fit..or should i go bigger?

Will this item make my bum look flatter?

Can this be worn under tight trousers?

How do I go about exchanging it for a smaller one????