18th Century bed gowns or short gowns are super simple pieces of clothing. They seemed to be the kind of thing you’d throw on to do stuff around the house, or if you had to run to the store. Not your best clothes, but you wouldn’t be embarrassed to run into your mother in one.
One shown here by M. Garsault has a pleat at the back, and at the waist.There are also great examples in Fitting & Proper, and Costume Close-Up: Clothing Construction and Pattern, 1750-1790.
The design is simple, and examples are in lightweight fabrics which make it perfect for smoldering hot summertime reenactments. My red one is made from a linen blend, with silk ribbon binding the edge. The Indienne (Persian printed cotton) one is basically the same, just a little shorter.