Antti,
The hub carriers, or uprights, or whatever they are called, the big cast iron piece where you insert the bearing outer races, should be a tight fit to the bearings. These don't wear either so something is wrong. As these don't wear, second hand ones should be fine.
The hub itself is the rotating part. These can wear badly if a bearing is driven too far before replacing. This would affect the fit of the bearing inner race and overall tightness when the axle nut is fully tighhened.

Have you measured that the disc is really warped? It's a common myth that juddering brakes are always casued by warped discs. It can also be because the surface of the disc has uneven friction. This can be caused by glazing or burned pad material. This is a problem that I had with early greenstuff pads that kept "coating" the discs.