Pascal’s option here is the simpliest. But, I did want to point out another option is to use the Quadremesher and the SubD tools in the Rhino 7 WIP. This leads to a lot of ways to edit these forms.
You can find out more about the SubD here: Rhino 7 Feature: Subdivision Geometry
Here is how Meshes to SubD can be converted: https://www.youtube.com/watch?v=_rE8lsKdd6E&feature=youtu.be
And the here is a new draft of a tutorial on getting these shapes with SubD: https://wiki.mcneel.com/7/tutorials/subd/mouse#overview