I've been making my own cotton nightgowns for about 20 years. The other day one of my old nighties started to shred as I was putting it away (it was 8 years old) and I knew it was time to make a couple of new nighties.
The pattern I use is, now you will probably laugh at me, Butterick 6886, which is a maternity pattern. It's really comfortable. The pattern makes a sleeveless nightie and a robe. The nightgown is really simple to make, the hardest part for me is the bias tape binding around the neck and arm holes because I make my own binding from the same fabric and that takes some time, but it looks really nice.
I just ordered two fabrics to make my new nighties. These fabric were on sale and will be perfect for my project. I'll share the finished nightgowns when they are done.