Measure the route before you measure the room

Most sofa regrets begin at the front door, not in the sitting room. Before you fall for anything online or in a showroom, walk the delivery route with a tape measure and note the narrowest point of every doorway, hallway bend, stair turn and shared entrance. A standard internal door frame gives you roughly 76cm of clear width, but an older property with a narrow frame and chunky architraves can pinch down to 70cm or less. Don't forget the door itself — take it off its hinges if it helps — plus radiators, banisters and that awkward turn at the top of the stairs.

Next, measure the sofa's smallest dimension, not its width. A sofa that's 95cm deep won't pass through a 76cm doorway upright, but laid on its side its height might be only 80cm once the legs are off. Look for screw-in legs you can remove in a minute, and check whether the back bolts on separately. If the numbers are tight, a flat-packed design that arrives in two or three boxes can be a genuine solution rather than a gimmick.

Work out your walking space, not just your wall space

A sofa can fit a wall perfectly and still ruin a room. What matters is the space left over once it's in place. As a working rule, allow 60cm to shuffle past, 75cm to walk comfortably, and 90cm if it's the main route through to the kitchen or stairs. Leave 40–45cm between the sofa's front edge and a coffee table so you can actually sit down with a mug of tea without cracking your shins.

In a room measuring 3.5m by 3m, a 1.9m sofa against the long wall leaves over 2m of open floor — generous. Push that same sofa into a corner and add a chunky armchair and a side table and you'll be shuffling sideways. Before you buy, mark the footprint on the carpet with masking tape and live with it for an evening. It feels slightly daft and it saves an enormous amount of bother.

Slim arms, raised legs and shallower seats

The bulk of a sofa is rarely the seat — it's everything around it. A rolled or chunky arm can swallow 20–25cm on each side, which is 40–50cm of seating width gone before anyone sits down. Slim arms of 10–12cm give you back most of that. Seat depth matters too: a standard 55–60cm is fine, but a shallower 50–52cm seat reads as less hulking in a small room, even if it's less suited to full-length lounging.

• Aim for an overall depth of 80–85cm rather than the usual 95–100cm.
• Choose a low back — around 70–75cm — to keep sightlines across the room open.
• Look for legs of 12–15cm so light and floor show underneath. A skirted base sitting flush to the carpet makes any room feel smaller.
• Two-seaters of 1.5–1.7m long are the sweet spot for most terraced sitting rooms.
• Check seat height: 42–45cm lets most adults put their feet flat on the floor.

Removable covers are the thrifty move

In a small room, the sofa is usually the biggest single item you own, so it should be the one that lasts. Zip-off, machine-washable covers are the single best feature you can buy for the money. Spills, muddy paws and the slow grey tide of everyday life all come out in a 30-degree wash, and a mid-tone cotton or poly-cotton blend will survive years of it. Read the care label before you commit: if it says dry clean only, walk away.

If the budget won't stretch to loose covers, a fixed sofa plus a generous throw over the seat cushions is the honest halfway house. Fitted stretch covers are fine as a stopgap but tend to shift and ping off the corners. If you can afford a spare set of covers at the point of purchase, buy them — they'll be discontinued long before you need them.

Choose the seating that fits real life

Two genuinely comfortable seats beat three squeezed ones every time. A two-seater with a slim armchair in a different spot gives you far more flexibility than one three-seater dominating the room, and you can move the chair when guests come round. An ottoman with storage inside does double duty as a footstool, a temporary seat and a home for blankets. Sit on the thing before you buy it if you possibly can — fifteen minutes, not fifteen seconds — because a sofa that looks neat and upright in the showroom can be a misery by the second cup of coffee.

Finishing touches that keep a small room feeling open

Pale and mid-tone upholstery reflects light and makes walls recede; very dark sofas in small rooms can feel like furniture with the lights off. Keep the rug large enough that the sofa's front feet sit on it, ideally leaving 15–20cm of bare floor around the edges, and choose a rug that echoes your wall colour rather than fighting it. A mirror opposite the window bounces daylight into the darkest corner, and two or three cushions in a fabric you love will lift a plain cover without costing much. Small rooms aren't a compromise — they're just less forgiving of guesswork.