Should I get hair extensions or hair piece?

My hair is shoulder length but it is very short on top because of a disorder I have. It's all growing back in after being bald. My hair is only like 3 inches on the top and I'm considering getting hair extensions so I don't look like I have a mullet. Any suggestions on how to go about this and whether it would be easier to buy clip-ins? Where can I do/buy this?