You can't use the Jupiter 12 on the post war Contax IIa and IIIa, as the big bulging rear element hits something. You can use it on the pre-war Contax II and III, and all Kievs.
I have been thinking about this issue a bit. I recently obtained a Kiev 2a, and it's a lot of fun. Mine came with the Jupiter 3 50mm f/1.5. All of it was from fedka, and everything works great. So, I've been thinking about the Jupiter 9 85mm f/2, and the Jupiter 11 135mm f/4. These lenses are the pre-war Zeiss designs, just made in the then USSR.
I've had so much fun with the Kiev that I'm tempted to purchase a Zeiss IIIa. One option for wide angles is the Cosina Voigtlander SC line that is sold by cameraquest. Focal lengths offered are 21mm, 25mm, 28mm, 35mm. They are for the Nikon rangefinder, but with wide angles, the small focus discrepancy between the Contax and Nikon's version of the Contax mount shouldn't matter.