I started with the bodice pattern from Butterick B5181 (which the cat promptly destroyed) and the sleeve pattern from New Look S0597. I had to cut the sleeve down a little, but it worked pretty perfectly. I will likely end up shortening the sleeves to just above the elbow or shorter.
I ordered some stretchy cotton/spandex from Ebay for about $30. The seller's username is koshtex.
The fabric was heavier than I wanted. I was hoping for something thinner and drapier, but this will serve for the moment.
Working with stretch knits has been quite a learning curve, and there are definitely things I would do differently - like wait until the entire bodice was assembled to hem the neckline - but overall, this went together relatively quickly and easily.
For the skirt portion, I took a measurement around the ribcage: 36 in. My intention was to create four trapezoid shapes with a gusset in the back for extra drama. 36/4 = 9, plus 1.25 seam allowance.
The back of the bodice ended up being a bit too big, but the overall shape of the skirt is fantastically full. I think I will wait to make any tweaks to the fit until May. Next up is a hooded scarf to go with it.