We have a Murphy bed in our B+ unit and like it very much. It is a queen residential style mattress, not a flimsy pad or a bunch of cushions pushed together. It is very simple to set up/put away the bed - takes about a minute.
The only drawback is that you have to have similar sleeping patterns. A bed takes up so much room when it is only used for 8 - 10 hours. If you are looking for a short unit, this is one solution - lots of floor space, comfortable bed, allows for a really decent bathroom, functional kitchen and plenty of storage..