I suggest going to Pottery Barn or Sure Fit online. Both have varying sizes, styles, and prices.

http://www.potterybarn.com/search/siipcovers/furniture/results.html?N=4294966985&cm_sp=OnsiteSearch-_-GlobalNav-_-Button&type-ahead-viewset=ecom&words=siipcovers

http://www.surefit.net/

The problem with slipcovers on sleeper sofas is that you have to remove it whenever you need to open the sleeper...
...and IMO, one-size-fits-none slipcovers only look good in the catalog - once you sit on them a couple times, they're a hot mess.

Personally, I'd just toss a nice large textile such as a woven shawl, throw or woven rug over the back of the sofa.

the dog is cute to!!

this picture makes me want to curl up with this dog on that sofa with that cushion and throw :)

Custom at an affordable price - www.needleandshears.com