To get this lovely period rear view, I made a bum roll using Margo Anderson's Elizabethan Lady's Underpinnings Pattern. I think it worked out well!
Here's another shot of my oh-so-curvy silhouette as well as what the bum roll actually looks like:
It's made out of basic printed cotton and stuffed with polyfil. I kept the stuffing pretty squishy so that it would look a bit softer than an Elizabethan bum roll and wore it slightly below my waistline since the style of dress I'm wearing (anglaise) has a great pointed look down the center back. The bum roll helps to poof out the back pleats. And poof it does!