Where can I find a plain cotton sleeveless knee-length nightdress?

[NCG161280]

Please help. I’m trying to find a nighty that is:
100% cotton
Sleeveless but not strappy i.e not with adjustable straps that slip
Not white
Has no bows or cartoon characters on it
Doesn’t look like a Victorian grandma would wear it
Knee length
Size 18/20
I have looked everywhere!

Toast do them. Sizing is huge so even if you don’t think they have your size, a large might well fit.