I have a Yashika FX-2 that I bought back in the 70's. I would like to upgrade the body to a digital form and I'm not sure which ones I can buy. I have several different lenses and I really don't want to re-buy them for a new camera.
Yashica/Contax mount lenses will mount cleanly on Canon DSLRs (in all-manual mode, of course) with a glassless mount converter if you want to stick with a traditional SLR form factor due to Canon's short flange-to-film distance and large throat. Use on other DSLR mounts will mean either loss of infinity focus or an optical conversion group. Mounting the lenses on a mirrorless camera (μ4/3, etc.) is mechanically easy, and mounts should be available, though not all cameras will work well with a manual mechanical lens.
No digital cameras use the Contax/Yashica mount directly (Kyocera never got into the dSLR game, despite owning the mount system), but with adapters, they can be used on a variety of digital SLR and mirrorless bodies, with a few caveats.
All mirrorless bodies (Sony E-mount/NEX, Fuji X, Samsung NX, micro four-thirds, etc.) can easily adapt C/Y lenses with simple ring adapters, and they're widely and readily available through a number of resellers.
With dSLRs, however, some of the digital mount systems have a deeper "registration distance" (the distance the mount holds the lens away from the image plane/sensor) than C/Y, and since you can't just shove a lens farther into a camera body, and an adapter always adds to the distance, you have to find an adapter with a glass element in it to act like a short teleconverter, or use a Leitax lens mount replacement, if you want the lens to focus to infinity for all the dSLR mounts except Canon and Panasonic/Olympus four-thirds dSLRs. And the glass element, particularly for an inexpensive adapter, can affect image quality adversely.
Also, Canon's prosumer full-frame bodies (e.g., 5D, 6D) may have mirror clearance issues with Contax lenses. I'm not sure about Yashica, but I'd assume the same there, too. The Canon crop bodies and 1-series pro cameras typically do not have mirror clearance issues.
Whatever type of adapter you use, however, there is likely to be no electronic communication between the lens and the camera, and since C/Y was a manual-focus mount, lenses will not autofocus, will not have aperture control from the camera body, or report any lens EXIF information (e.g., focal length, lens name, aperture setting used, etc.) In addition, some cameras may not meter accurately, as not all bodies perform stop-down metering (I only have experience with Canon dSLRs and Panasonic mirrorless, but both are fine with adapted lenses; but Nikon's entry-level bodies are not).
In short, unless you've got amazing pro-grade lenses, it may actually be more worthwhile to save up and purchases native autofocusing lenses in whatever digital camera mount you end up purchasing, unless you're someone who loves vintage glass, or is just plain stubborn and likes to do things just because you can.
I use Contax lenses. I have try them on different Canon body but they all have metering problem when stepping down (see this question How can I work around metering issues with adapted lenses on a Canon DSLR?) Glass free adapter conversion to Nikon or Sony is not possible.
On the other hand I'm using them happily with a Olympus E620 (ok this body is not very good above 400ISO but I can deal with it) and a fotodiox ring with dandelion chips. Of course I do step down metering. You can have a look at my gallery http://www.dubath.net/Photos/index.php?/category/5 where all but few images are taken using the Contax 50mm1.7 /60mm macro/80mm 1.4/135mm 2.8
Another solution is to switch to mirorless. You will find plenty of adapter ring allowing to mount your lenses on more or less all the body brand.
Last but not least if you do not want to keep compatibility with your Yashica body there is a more radical solution: replace the mount you can find references here http://www.leitax.com/