Klick-Klack sofas & Jack knife sofas are not futons! They are small-scaled contemporary sofas that do come down or fold to make a flat bed. The are one piece, very firm to sit and sleep on and have no flexibility to interchange parts or looks. They are not full size anything. They run between a twin and full size bed and are hard to make up when opened.
We have customers come into our stores to purchase covers for them or new mattresses and this is not possible, because it is made in one piece and covered like a traditional sofa. Nothing is interchangeable. When a part wears out, that's it.
I do not know why stores call these futons because they are not! I guess it is ignorance on the part of the store or advertiser. Unfortunately this mix up causes futon stores problems having to explain to customers that they didn't buy what they thought they were getting and I feel bad about this.
A futon does have a frame, a mattress and a cover selection from which you can customize your look and comfort level. And you can do this within your budget. If you want to change anything later that is always possible.
Please, stores that sell klick-klack sofas, call them what they are and don't confuse your customers. This is false advertising.