The right size is not the comfortable size
Choose them in the size where the waistband pulls slightly: it must do its job and keep the shorts in place on their own, without relying on the drawstring. On the mat the slimmer look disappears completely. If in doubt between two sizes, choose the smaller.
Garment care
At 30 degrees, inside out, no fabric softener and no tumble dryer. Heat is the main enemy of the waistband.