"thicken" convoluted surface

I have a convoluted surface that wants to be printed. I have come up with several methods but none that do not require significant hand tweaking to get something that is closed and not self intersecting. Goal is to have the result be thin (e.g. .5 to 1mm) - clearly it is not possible to have all areas the same thickness rather want nothing less than the minimum. Quite possibly I am overlooking an obvious method...