I've bought at least 2 covers from Boat Covers Direct.
They have a great pulldown menu system where you plug in your dinghy or small boat and model, and they typically have the exact fit for that dinghy.
They typically have about three quality/price levels. I cheaped out the first time and picked the lowest quality. Understandably after 1-2 yrs in hot southern sun, it started to tear a bit- my mistake. However, when I contacted them again, they actually gave me credit for the cheap one under partial warranty and gave me a great price on the higher quality cover. The new one I think the fabric is called Sun Dura and its going strong. No affiliation with the company, just a satisfied customer.