Are you using a digital micrometer and measure exactly? If so, remeasure again, but this time measure the diameter of the seat post and shim as one unit. Then ditch the shim and just get a post that fits your seatube. You would be best off going to a bike shop, they have a tool to measure the inside of a seat tube exactly, and can tell you what size post you will need.

Bike was very likely not made in Switzerland. Peugeot made bikes in France, and for a couple of years, they came with Swiss threaded bb. Its a curse.... Motobecane did the same thing, only Motobecane did it for many years.

Its kind of like English threaded bb. Bike might be made in China, but it will come with english threading.