Short answer. Cheap stretch does. Better fabric recovers. If the knee bags after three washes, the cloth was never going to last.
Fit in real work, not in a mirror at home
The only test is a squat, a reach, and a sit. If the garment fails one, it will fail at hour eight.
Start with The Classic if you want a true two-piece, The Jumpsuit if you want one piece, or The Fashion Flare if you want a line through the hem. Then use the size guide.
