First, consider the weather in your area. If you live in a colder climate, you'll want a coat that is thick and insulated to keep you warm. Look for coats made with materials like down or synthetic down, which provide excellent warmth without adding too much bulk. You should also consider coats with a hood or a high collar, which can provide extra warmth for your head and neck.
Next, think about your personal style. While function is important, you also want a coat that looks good on you. Look for coats in colors and styles that flatter your body type. If you're not sure what styles look best on you, consider asking a friend or family member for their opinion, or visit a clothing store that specializes in big and tall sizes for advice.