[Brightcolours]

Arthur, I use a DSLR (Canon EOS 6D) with quite a few of my lenses being manual focus (Voigtlander 20mm f3.5, Micro-Nikkor 55mm f3.5, Canon FL 55mm f1.2, Nikkor-S 55mm f1.2, Nikkor-H 85mm f1.8, Nikkor-Q 135mm f3.5, Nikkor "K" 135mm f2.8, to name a few). Because of the larger aperture MF lenses, I put a Canon Eg-S focus screen in it, which shows the DOF more accurately, especially for manual focus. I find it practical enough, it seems like what you want already exists, especially since the price of the 6D has come down a lot.

 

Manual focus lenses you can put on the 6D: EOS EF mount, Nikon F-mount, Olympus OM mount, Pentax PK mount (after some slight modification), Contax/Yashica C/Y mount, Leica R-mount, M42 mount, Tamron Adaptal mount. You can convert the mount of many Canon FL/FD mount lenses to EF mount, and some Minolta lenses.