Well as this thread refuses to die I'll comment.
I used to be an Interior Designer and I sold Collins and Hayes furniture in a very previous existence. This sort of furniture is a quality investment - the sort that you only make once or twice in a lifetime! However Modern flame retardant foam filling is not as long lasting as old fashioned materials, (but it is more comfortable) so you need to replace the filling as well as the covering material. The frame should be good for 25 years at least unless you play after dinner rugby games!
If you go back to the original manufacturer they should have templates for the fabric covering which will save time and therefore money, but the cost of transportation may negate the saving. A good local upholsterer may be the same or cheaper after transport.
The cost of re-upholstery is about the same as the purchase price of a cheap new sofa, so it isn't worth re-upholstering a chain store sofa, but on a quality piece you should get exactly the same wear as from the original incarnation - ie another 10+ years or so. (A chain store sofa frame isn't intended to have its life extended by re-upholstery)
A cheap sofa can be given a whole new lease of life if the filling is ok, by buying loose covers from one of the national companies that advertise everywhere. These send a chap round to measure up and use their own fabric. The fit will be very very good. Sadly a local upholsterer will not be able to achieve such perfection at a cost effective price.
A sofa that has been saggy for years may have lost structural integrity as the framework relies on the support of all the webbing, stuffing/filling and tightly stretched calico to hold everything together and reduce play and wear on the joints. If an upholsterer says it isn't worth recovering ask if this is what they mean.
I reluctantly parted company with my quality sofa after it had been used as a trampoline and bed by a generation of children, a dog and several generations of cats. I made my next purchase in the expectation that it will look good for 5 years and anything after 8 years is a bonus. As my tastes have changed and my comfort expectations risen, I was happy to buy new and I haven't paid the extra to ensure that I have the option of re-upholstering later on.
I'm going to re-cover my wing armchairs and I expect that they will see me out
. It is much cheaper to recover these than to buy new.