This one is by
Helly Hansen Workwear, made under licence by a Canadian company, Climate. It's polyester, which is not ideal, but I wear a merino wool base-layer, so it's not next to the skin. It's what I would class as a mid-layer, and I thought that "onesie" was the new name for the winter combinations that Grandad used to wear.
Whatever, it's indubitably quite the thing for cold weather sailing. Being no longer in possession of a waistline, I find a tight waistband is irksome, and this suit gets over that problem, with no disadvantages. The snug fit to the legs makes it easy to don boots.