Here's a step by step of what goes under the gown. A few pieces are missing, I don't have any drawers or pictures of an underhoop petticoat. My underhoop petticoat was actually made as a Regency waist petticoat, but it works for both eras!
I used the Laughing Moon pattern for the chemise and corset, and used the free instructions at Elizabeth Stewart Clark's website to make the petticoat. The hoop is made from a kit from Originals By Kay.
It should have sleeves, but it doesn't. The sleeveless chemise is a later invention...
Believe it or not, this is really quite comfortable! It just gives the proper support and line needed under a Civil War era dress.
The hoop and always curious Koshka. Yes, the hoop is unfinished. I will do that someday, but it is functional for trying things on! It has a 108" circumference.
These pictures are a great example of why you need a petticoat over your hoops. Note that you can see the bones through it. This would be very tacky if it were a dress.