Make over your sofa by layering long and loose fabrics over it. You can make a loose cover by draping one large piece of fabric over the sofa and then placing a plus-sign-shaped layer of fabric over that. Use contrasting colours or patterns to add visual interest or stick to a solid colour or single pattern if that is more your style. You can also use only one layer if you do not feel like cutting and measuring so much fabric.
Measure the sofa widthways, from the bottom of one side, down one side of the arm, across the seat, over the other arm, and along the side of the arm to the bottom. This is the arm-to-arm measurement. Measure the sofa from the bottom centre of the front, back across the seat, over the top and then down the back. This is the front-to-back measurement. Also measure the width of the seat and the depth of the arm rests.
Cut a piece of fabric so that it measures the depth of the arm rests plus 5 cm (2 inches) by the arm-to-arm measurement plus 36 cm (14 inches). For example, if your sofa is 3.8 m (150 inches) arm to arm and 60 cm (24 inches) deep, cut the fabric so that is 4.16 m (164 inches) by 65 cm (26 inches). This is the arm fabric.
Cut another piece of fabric that measures the seat width plus 5 cm (2 inches) by the front-to-back measurement plus 36 cm (14 inches). If your front-to-back measurement is 3.56 m (140 inches) and your seat width is 1.2 m (48 inches), cut a piece that is 3.92 m (154 inches) by 1.25 m (50 inches). This is the seat fabric.
Cut the contrasting fabric so that it measures the front-to-back measurement plus 30 cm (12 inches) by the seat width plus twice the arm-to arm-measurement. For instance, for the sofa that is 3.81 m (150 inches) arm to arm, has a 1.2 m (48 inch) seat and is 3.56 m (140 inches) back to front, cut a piece that is 3.86 m (152 inches) by 8.82 m (348 inches).
Fold the four edges of the under fabric over 1.3 cm (1/2 inch), then another 1.3 cm (1/2 inch) and pin in place. Stitch along the edges, removing the pins as you go.
Drape the under fabric over the couch, arranging it so that it hangs evenly and neatly.
Fold the four edges of the seat fabric over 1.3 cm (1/2 inch), then another 1.3 cm (1/2 inch), pin and stitch along the edges. Repeat with the arm fabric.
Drape the seat fabric over the front, seat and back of the couch. Place the arm fabric over the seat fabric, so that it hangs over the arms and forms a plus sign with the seat fabric.
Tuck the extra seat and arm fabric into the sides and back of the couch cushions, until the fabric just skims the bottom edge of the couch.
To reduce the need to measure and sew, you can replace the under fabric with a queen- or king-size bedsheet.