I found the option to make more complex round forms in Solvespace version 3, the one in some repositories is 2.3 (e.g. Raspian). Not sure if it's in these old versions. I'm using the version from Github now, which even builds on a Raspberry Pi 3 directly. It can create a helix or revolve around some point, but not completely. I want to use this to build many parts which will assemble to something bigger, for example a skull or a abdomen. Only if absolutely necessary their should be some small parts added which a sculpted. I want everything in CAD (parametric design), so I can add cavities and then holders or levels on the inside, or scale and slice the whole thing however I want to.
The example pic with the abdomen is from Sophie (stl-file in the Mega cloud of the developer). The green part is a example in CAD, which isn't perfect, but it shows that I might be able to build something alike step by step. This might also be more useful if something is supposed to be a mold for silicone rubber, bc I can work on the inside of such a model by making a cavity with the same shape but maybe some extras like the negative of the belly button.
I'm still playing around and learning, so don't hold your breath for something complete coming very soon. I'm working parallel on may different parts, however I feel like. I found that in some cases it's good approach to use the 2D preview of a stl-file in a slicer to get some picture with a pattern as orientation. Also using 3D sculpted models for comparison.