So I've sent off for some French terry with lycra from Ikasyr in Finland! To see if I can make my own.
New discovery – sweatshirt fabric is also called "French terry", so searching for French terry dress can get results. This is by splendid and I like the aubergine colour.
J Crew do them too.
Trust Cos to create the perfect simple shape – but it's blue (I want grey or black).
There are a lot of sweatshirt dresses in the high end of the market, like this James Perse beauty. Again, expensive/sold out in large.
Anthony Thomas Melillo sweatshirt dress – I love this because it's nice and long, but it's expensive and sold out in my size. (A common theme)