Ursula is a basic, highly-customizable undies pattern. Here are some of the early versions testing different combinations of options, which may be useful to you as you design your own pairs.
This (yellow with blue elastic) is a basic Ursula with the default options. It is a lowish-mid rise with moderate front and back coverage. The fabric is a modal spandex knit and the elastic is fold over elastic, so the seam allowances were trimmed away.
This (white with black elastic) is a thong Ursula with high back exposure. Specifically, these options were changed from the defaults:
The fabric was a remnant and turned out to be a poor choice of fabric for this because it was too thick and not stretchy enough. The elastic was 0.5 in (1.27 cm) which was probably too wide. This probably isn't the "ideal" thong version but hopefully these notes are a helpful starting point.
This (yellow with black elastic) is a low rise Ursula with slightly higher coverage. These options were changed from the defaults:
The elastic was probably cut too short, contributing to the waviness. However, the fit was great. This is a modal spandex knit.
This (yellow with burgundy elastic) is a high rise Ursula. It used these options:
The fit is truly high waisted, slightly above the belly button on the tester, and very comfortable. This is a modal spandex knit.
These last two (gray and blue, gray and burgundy) were early test pairs of Ursula.
These pictures were shared on the FreeSewing Discord and are reposted here with permission.