Can any Harry Potter fans please help me with decorating ideas?

I’m in charge of getting decorations for a little guy’s 7th birthday party. It’s Harry Potter themed. Without going too nuts and too over-the-top expensive, the idea is to decorate the house like Hogwarts.

I’ve never read HP or seen one of the movies, and frankly I have no desire to.

Can anyone please give me some tips on what the heck I’m supposed to do or buy for this?

Thanks!