All kinds of new possibilities for extra beds have begun to appear on the market. There is a reason for this sudden popularity, and that is the steadily shrinking floor space of the average new American home.

As our homes began to grow smaller, the guest room was the first to go. Often it was combined with the family room, or the study or library, in an attempt to keep an extra sleeping space available for night visitors. Even the living room of some homes has to do double-duty these days as a guest room.

In a living room, I designed for a young, newly married couple, I was asked to provide an inexpensive solution for the guest room. The apartment had only one bedroom, and that was small. So we decided that the living room, the only other space in the house, would have to become a sometime-guest room.

The ideal solution was to combine the sofa and the bed. Not wanting to splurge on a sleep-sofa, which at a minimum costs about $350, I chose a "full-size" box spring and mattress. This could easily sleep two, yet, at 54-inches wide, it could also become an acceptable sofa. Besides, it was a family leftover, and therefore free.

I upholstered the spring in an unbleached muslin, an inexpensive fabric that is sturdy and has a pleasing texture. I used the same fabric to make a contour cover for the mattress. This has elasticized corners and is just larger than the mattress itself to allow for the sheets and blanket that lie beneath it, ready for the unexpected overnight guest.

I bought a few oversized pillows and covered them in the same muslin. Two ivory pillow cases, to match the sheets under the cover, are used to accommodate the necessary bed pillows; two darker occasional pillows complete the group, providing enough back support to make the deep bed usuable as a sofa.

Because the room had an eight-foot ceiling, and because I liked the low look, I placed the box spring directly on the floor. If your room has a higher ceiling, you can build a low platform of 1-by-4's and plywood to fit the box spring, or build it higher and do away with the spring altogether. Springs, by the way, are no longer box springs, but merely "boxes" that have no resiliency; you can make them yourself, and far less expensively.

To keep the room simple, yet inviting, I flanked the bed on one side with a wood chest (which holds extra blankets and sheets), an inexpensive set of coffee tables that can be reconfigured, for dining, and a reproduction Brighton chair made of bamboo.