First, I'd find something inexpensive that brings you joy. Maybe a house flag that represents your house then use those colors as a base for buying something that matches, like a yellow blanket if you are hugflepuff, or a red throw to put on your bed if you are gryffindor. Then see what you can make yourself. For example, I made a little book into a book that says Secrets of the Restricted Section by printing a book cover on sticker paper. More on reddit.com

I couldn't find this, but what would be really cool is some rebound versions of Harry Potter books for a coffee table as decoration? Like leather casings so they look simple on the outside until you crack them open? More on reddit.com

Check out Harry Potter party ideas on Pinterest. More on reddit.com

No specifics, but my advice is to ask yourself, "Do I want decors that look like what one might find in that world, or do I want blatantly Harry Potter merch?" Personally, for my own home, I avoid the latter because I want it to be a home, not a themed park. For example, instead of having a Slytherin poster, I might feature deep green velvet curtains, moody lighting, maybe a little silver snake doorknob or drawer pull, stuff like that. Basically, a home that looks like it could be something out of HP's world, rather than a teenage fandom bedroom. Not that there's anything wrong with that, it's just that I think it's good to decide which direction you'd like to go towards before deciding how you'd like to decorate. More on reddit.com