I bought a couple of budget priced 2 seater sofas from Sofa Sofa a few years back. They were well made, except for the cushions, which went flat went sat on for a short time. Yes, there were instructions included that stated the cushions should be plumped up every day, but this really didn't make any difference.
In the end I had quality foam cushions made for me by a local upholsterer. They did cost �35 for each cushion, but it was worth it - it's like having a new luxurious suite.
I only wish I did it earlier.