I have a love seat that I use as my couch. I got it second hand and it works just fine for me in my small space. It also folds out to a single bed, handy for the odd guest that stays over.
The back cushion for the love seat was made of fiberfill and lost it's umpf and cushioning a long time ago. And one of the dogs decided the cushioning would make a great play toy and shredded half of it as well. I decided to replace it with some sturdy upholstery foam. Until I went shopping and found out that the high density foam I wanted would cost around $70. I also needed to have the cushion cover repaired replaced. The fabric around the zipper had worn and torn, the whole assembly was not good. I was quoted at least $30 to fix the zipper and "remake" the cushion cover by the seamstress at the dry cleaners. I was also not prepared to spend $100 on a new cushion for a used couch.
The solution came to me this weekend while at TJ Maxx, just browsing the isles. I was pricing out accent pillows to use as the cushion. I was not impressed by the choices left (wrong color, ultra shiny fabric, wrong size), but a trip down the sleep isle yielded a two pack of European Sized Bed Pillows (26 x26) with a plain white cover for $19.99. The pillows fit nicely side by side on the couch, provide enough cushioning and best of all, the cost was $19.99. I should have enough fabric from the old cushion cover to make covers for the new pillows. If not, I can pick up a couple yards of fabric in a complimentary shade and make a "front side" and a "back side". For less than $30 and about a hour on the sewing machine, I've just saved myself $70 and I have spiffy new pillows as well.