You are really putting a lot of extra work into something that was probably an issue with your slicer or your filament. They're supposed to be thin, it reduces weight. You're going to make a VERY heavy headbase if you print it twice as thick.
but also
MeshMixer> Edit> Make Solid > accurate, accuracy/density 300-500, offset 0.8-1.6> plane cut to reflatten the bottom
would not recommend unless you're doing a foaming or spongy TPU print, and you will need to print the eyes smaller and nose/eyelids bigger (if you're good at math, you can math it, if you can't do math just print a few different sized versions at low quality to figure out the size)