While I do have a Regency shift already, I was the first one I made from cotton/poly broadcloth and the entire thing is machine sewn. As a result, it is very bulky, not breathable, and very stiff. The neckline is also cut very high and sometimes peeks out from my dresses.
Originally I had used Sense & Sensibility's Regency Underthings Pattern, but I opted for the Laughing Moon Ladies' Regency and Romantic Era Corset, which includes pattern pieces for a shift.
Just like the reviews, the back did run high. To help adjust this, I added 2" to the back of the shoulder strap pieces, and lowered the top edge the same amount to accommodate the change.