I was going to say Blender in a comment but you've mentioned it already.
Ease of use is most important. I tried blender and was blown away by the interface.
Blender can also be run almost completely with Python, if you are comfortable with Python then you almost never need to use the GUI or touch a mouse, which I also find intimidating.
update: I ...
I would suggest trying Houdini. You can create an inflatable balloon object out of a mesh with any properties you desire. There is actually a beginners level tutorial that shows how to do exactly what you are talking about. An apprentice edition with very few restraints is available for free.