Revisit the store where you bought your sectional. Several brands or stores offer ready-made covers for items they've sold in the past. Make sure you know the make and model of your sectional.
Search online for websites selling slipcovers. Measure your sectional accurately. If there isn't a cover for your exact sectional, you may be able to find a generic slipcover that fits.
Order a custom-made slipcover if you can't find a ready-made one that fits adequately. While it is a more expensive route, it is still cheaper than reupholstering. You will be able to choose the exact color and texture you want and be sure it will be a perfect fit.
Use blankets and pillows. While these are not snug-fitting solutions for covering your sectional, they can give it a whole new look and offer protection. A strategically placed giant blanket could be just the thing you're looking for, and it couldn't be more simple.
Sew your own slipcover. If you are handy with measurements and a sewing machine, you might consider whipping something up yourself. While the awkward shapes of a sectional can present a challenge, the custom look can be worth it. If you aren't a sewing genius, ask a handy friend who may be willing to help you out.
Reupholster the sectional. This is the most expensive route by far, but also will produce the best result.