complex surface shelling

 From:  malvin
I need to give thickness to the complex surface (please see the attachment).
I have tried "shell" command
It did not work exactly for the thickness I need (2 millimeters).
I understand why - according to some of the explanations in other topics the planes/radiuses are too small to calculate a certain thickness.

Is it possible to produce something like "smart shelling" - to give some thickness to this or similar surface?
So that planes that interfere with each other would merge and create one solid.

I need at least 2 point thickness (millimeters)

The overall task is to reduce a jewelry piece to minimum weight so I have to cut out and remove 3D areas in a ring/pendant/bracelet that are too thick.
Ideally every wall has to be 1.5-2 mm thick. Narrow areas would merge.