As a very early Christmas present, my wife bought me a dress form! It's an adjustable one from Dritz.
I started by turning dials until the form was about 1 inch to 2 inches smaller than my measurements.
Then, I took wide tape and covered all of the gaps.
I added a bra and padded it out a bit.
Then, it got a little weird. I made a booty for my dress form using layers of bonded quilt batting. Also, some back fluff, because, let's be honest, I have some.
Tummy fluff added.
I used plastic wrap to cinch the waist in. The angle between the bottom of my ribcage, the center of my waist, and the outward curve of my hip is very sharp, so this is actually a pretty good approximation.
Ta da! I thought about making an actual form cover, and I may, someday, but I decided that I'd rather spend my time sewing things that I will wear vs. things for my dress form to wear. T-shirt to the rescue! Bonus cat-themed skirt from semi-failed cami-sewing experiment.
It's not perfect, but it's better than just guessing. I added a pin to each bust apex, to make them easier to find.