Sci-fi shows have the ultimate water-bed: a large water filled tank in which floats the subject, probably for medical regeneration or such.
It sounds comfortable to me, bringing back all kinds of memories of swimming pools, and floating in them. However, breathing is an issue. We humans cannot breathe under water. A null issue in Sci-fi, since it's always implied there that they have extra-corporeal breathing and circulation: basically their blood is being oxygenated outside the tank and then re-injected. (A tad extreme for a bed, ya think?)
So for a bed version, I would have a strapped-on oxygen mask attached to a tube, attached to an air-pump, a-la a CPAP machine. This is dependent on power, so in case of power failure, there will be an uninterruptible power supply, and instructions to drain the tank should the power fail. We can refill it if the failure proves temporary.
The tank fills from above, adding a certain amount of sea-salt for buoyancy. The user is put in from above (I guess you climb stairs to go to bed?), deploys the mask, and starts the air pump. The pump shoves air into your lungs through the mask, and exhalings bubble out of the mask into the water, where they rise to the surface. After eight hours of sleep, the tank drains from an openable vent at the bottom, into the sewer, the user climbs out through hand-rails or a cord, and the tank is cleaned, perhaps through a water-spray.
A relaxing, if extremely weird, way to sleep.