Most sofas seem to have very wide arms, so that up to one third of the length, as it were, is arms, not seating area.

John Lewis do the same sofa in a larger sofa, but it is a sofa bed. It is further complicated because I have two chairs in the lounge that are sort of a dark red with a bit of green and gold and orange, in a very modern leaf pattern. So finding an exact match in red is going to be impossible.
Having found out what a new sofa would cost in the right size, I could now find out if recovering the existing sofa, and replacing the foam in the seats, would be cost effective. Also if recovering a sofa there may be more choice of colours. The walls are very pale blue and the curtains are very dark blue.