I've heard paranoia of fish-cooking so deep that a friend believed that the fish would somehow ruin itself despite her best efforts. That was then. This is now. My friend loves to cook fish. It's so simple as to defy itself as a topic for this story.
Overcooking fish is more trouble than doing it fast and right.
Autumn is a great time of year for fresh fish. Not only is it low in fat and high in protein, the waters are cold and a huge array of fresh fish is available in supermarkets as well as in that antiquated retail source, an actual fishmonger. Maybe your city has stores specializing in fish. If so, shop there. Fish professionals love their specialty and will know specifics about freshness and how to describe the taste and texture of the cooked fish.