Can you tell me the best place to buy a coat for my dog? I would like to consider some interesting options.

I would recommend you to choose only clothes that are made with good quality and good materials. Because it should look very good, and it is not desirable to buy poor quality accessories. I would recommend that you look here https://bitchnewyork.com/collections/dog-coats good options for dog clothing because there's a really great selection and I think you'll find something to your liking.

Look at the options for your query on Amazon, I think you'll find something on this marketplace  there is a large selection.