You definitely don’t need two sizes up nor is it that tight. For reference I’m 5’4”, 200lbs and typically wear size 13 in FN jeans. I could’ve done my regular L or XL for room but to be safe (based on the reviews) I went up two sizes. It’s not that bad. But if you like your coverups to sit nicely, one size up is perfectly fine. There’s stretch with the waist. The thighs could be why you need a one size up

I’m 5’9” 200lb wide hips and big booty n thighs. Didn’t make it over my booty. Has very little stretch and the material looks like gold metallic strands weaved into black net - not my style. It looks better on the model. I passed them over to my friend who wears a large & 5’10” and she loves them just a little short on her.