Digital option

Canon is a good option for those wanting to make use of their YC lenses in front of a sensor. For many years, I used a Canon 10D for this, and it worked well. The down side is that you have only manual focus. Well, you have that on the FX3, but the difference is that in a digital body, which is always made for autofocus, there's usually no manual focus indicator in the viewfinder, like a split image prism or a microprism, as you have with most film cameras, so focus can be a bit more hit-or-miss. And don't think the LCD screen on the back is a sure guide, they're often very sharpened and high contrast, and can strongly mislead.

The other consideration is that most of the low-price digital SLR bodies have crop factor, because their sensors are significantly smaller than the area of a 35mm film frame, meaning that the effective focal length of your ML lens is increased by just over half. That means you can say goodbye to wide-angle. Or at least, a 20mm lens like the Flektogon will have a field of view that's equivalent to around 32mm in 35mm film terms. And your standard 50mm lens become equivalent to about 80mm.

You can still use auto-exposure, but only in aperture priority mode, since the camera cannot 'talk' to your lens and tell it which aperture to choose. You set the aperture, and the camera measures the light coming through, and sets the shutter speed. Note, of course, that it is now down to you to stop down manually if you have to, since you may need to focus at widest aperture then stop down manually to the taking aperture. That can rule out subjects where you've much motion to contend with, and hence changing distances.

Adapters are cheap enough, and from a pragmatic perspective, it's better to get three or four, and mount one on each lens you intend to use, rather than attempting to use just one adapter between several lenses 'in the field'. You want to keep a digital camera's lens mount opening covered as much as possible, to keep dust away from the sensor. So rapid changing times are really essential.

I don't know what your budget is, but if you want your lenses to preserve their nominal focal lengths, you need to look at so-called 'full frame' SLRs, like the 5D. I bought one of these fairly recently, though I've still to put it through its paces.

There's not much to add to alex' comprehensive answer. I, too, highly recommend getting a full-frame camera for manual lenses.

I've been using a Canon 5D with manual lenses for years, and I've been very happy with it. The 5D ("classic", ie. not Mk II or III) is quite old now, but used prices are low and it's probably the cheapest option for a full-frame DSLR. Plus, it is very robust, "pro" quality and will probably serve you many years. Get an Ee-S focusing screen for manual focusing.

The other option would be a Sony A7 (or A7s, A7R, -II, whatever). More modern, more pixels, more expensive. The Sony has no mirror and it's size is very much like your FX cameras, much smaller than the bulky Canon. If you plan to dive deeper into the world of classic lenses, the Sony is more versatile because you can adapt almost any lens to it (it has a shorter register distance than Canon, so it's easy to make adapters).