Make sure you choose the right model
If you get a different size for your hips than for your buttocks, take the hip size!
Joggers are made BIG, don't take a size bigger to have joggers take it easy,they already are. On the other hand, you can take a size smaller for a more fitted joggers.
Nightgowns have a cutoversized,they are loose and ultra stretchy. Don't take too big. If you want a slim fit, take a size below the chart.