Urban CoCoWomen's Elastic Waist Stretch Bodycon Midi Pencil Skirt

If I am 5'4 and weigh about 120 lb but I have a pretty good size butt, what size would I need without it being tight at all?

How form fitting is this skirt? Does it hug around the hips a lot?

Has anyone worn undergarment like spanx underneath?

i weighing 130 lbs 4’11 what size it will fit