As an ornament, the sunglasses receive more and more popularity in summer for not only the protection of eyes from UV but also the beauty of face. However, your problem is that your nose is a little big. You want to make it look slimmer by wearing sunglasses. I have the same problem, too. And I buy the sunglasses which are designed in cambered surface which will make my face show in the three-dimensional way. The nose will stand out and look slim from whatever the flank side or the front side. You may have a try.
To make your big nose look slimmer, you can try light wire- framed glasses. If you have a big nose, you can try some sunglasses with big frame and big lenses so as to make your bog nose less noticeable. Anyway, you shall try on some sunglasses in different types of frames in local shop so as to know what sunglasses look good on you.
Based on your description, I am aware of your intentions. However, choosing glasses needs to consider a number of factors, including facial features, skin color, the shape of face, and so on. As you said, your nose looks big, and you want it to look slimmer. Maybe you can try the rough frame glasses and slightly wider spectacle frames. From a visual perspective, they can modify the nose, that is to say, it can help your nose look slimmer.
As you say that your nose is big and you want to wear some sunglasses to make big noses look slimmer, you can wear large oversized sunglasses to add balance. In other words, large oversized sunglasses can make your nose slimmer. But Small frames will only accentuate it. While, you should also know that, when you want to look good, it isn't the business of your nose, but your face shape which plays an important part in the whole impression.