Pad your sofa bed mattress with a mattress topper. A quality, plush sofa bed mattress cover adds a layer of comfort--literally--between your guests and that hard metal bar stabbing them in the spine.
Stick an egg carton mattress cover below your sofa bed mattress for even more padding. It might look funny when you fold up the bed, but your guests will appreciate the comfort it adds.
Place a folded up towel or blanket directly on top of the metal bar of the sofa bed. This additional measure softens the feel of that bar as your guests toss and turn at night.
Make up the bed with soft, quality bedding. Using cheap sheets adds insult to injury, so stick with 100 percent cotton sheets with a decent thread count. You don't need to buy new sheets for the sofa bed--but if you're using sheets from your linen closet, make sure you select ones that will provide a luxurious night's sleep.
Serve a wonderful breakfast the next morning so that your guests will remember your hospitality--not their tossing and turning the night before.