The single sofa bed is a great piece of furniture; the difficulty is choosing between the huge range now available. First you need to consider the bed frame. There is no point in getting a sofa bed which is such an uncomfortable bed, otherwise you may as well just buy a standard sofa. There are two basic designs for the bed within a sofa.
The first is a pull out frame on which lies a separate mattress. The second thing to consider is the comfort of the sofa as a seat. With the foam mattress the seat is formed from the folded up mattress. With a sofa bed it is certainly worth considering buying one where the cushion covers are removable and washable. For example, a charcoal sofa with a deep red or green seat cushion will always look appealing.