A while ago I came across this cool program for designing chairs and other furniture – Sketchchair. While you could easily scale the chairs (or other furniture) to be human sized, I tested it by making some dollhouse sized items.
My first foray into the program netted me a clunky gaming rocket chair:
My second pass was actually a model downloaded from the website, which has a good number of community submitted designs, but adjusted to the size I wanted and material thickness I had available:
The third model I made was a sweet 80s inspired table.
The software will also run a simulation to see if the chair will be stable when someone sits on it.