The problem as everyone knows is the longer you are in a zero-g environment the more your bones waste away and your muscles become less efficient. My idea is not an ideal solution but hopefully it would be enough to reduce the problem on long voyages or time in zero-g. As the images show it's not much more than a revolving tube in which the astronaut would sleep, or if there are duties that involve interaction with a computer.

The Inner tube (blue edged) is large enough for an astronaut to stretch out there arms to touch a large touch screen on the other side of the tube. The screen is there to alleviate the feeling of being confined by allowing views of whatever is desired, be that sky, space, pictures of friends and family etc. its also there to allow interaction with the rest of the crew and ship systems, allowing work and rest in a simulated gravity environment.

The outer shell (red edged) would obviously be static.

Although quite large it wouldn't have to be heavy at all. And im sure the advantages would far outweigh the disadvantages.

You could even have sheets or a duvet for that feeling of being in a normal bed. If you had it slightly larger you could even have cohabitation!!

Im not sure of the stresses that would be transfered to the hull of the space ship, but if it induces a torsional twist to the ship maybe you could have another one next to it revolving in the opposite direction, if used im sure you would probably have more than one anyway.

Another plus is toilet time. although you would be in essence lying down, you could go to the toilet in gravity, which im sure would be a relief in more ways than one.

The images do not show a hatch, but a simple hatch would probably be needed to avoid getting dizzy if you looked up and out.

It would also allow for a limited range of exercise to help with keeping the body as fit as possible within the confines of the ship.

A small screen on the outside would allow shipmates to check on and converse with the person inside the faux gravity sleeping bag.

As stated earlier it isn't an ideal solution, but it is a solution.