The right sofa should fit your room, your doorways and the way you actually live. Before you buy, measure the wall where it will sit and leave breathing room on either side so the piece does not feel wedged in.
Next, measure your doorways, hallways and any turns or stairs on the delivery path, then compare them to the sofa width, depth and diagonal depth to be sure it will get inside. For open-plan spaces, a sectional or a 3-seater plus loveseat can anchor the room; for compact spaces, a 2-seater or a sleeper with storage keeps things flexible.
Finally, think about seat depth and height for comfort. Deeper seats suit lounging; firmer, higher seats are easier to get in and out of. When in doubt, tape the footprint on your floor before ordering.