Organization (by rooms, for example) and collaboration would be very useful features. Also a way to match things that go well together (maybe from other buyer's lists), and a way to add items you already have and maybe photos/videos of the rooms. But if you don't have a way to automate/make the buy easier, I still don't guarantee that I will order through you (especially if I choose 10 items from 4 sellers, I would loathe to then go to each seller's website and create an account there, place the order, add the delivery address and so on). And make sure you order exactly what you show on the website, as furniture is not as easy to return as a laptop - even if the seller's very helpful with the return, you'll probably take all the blame.
Your problem is, I only need to buy furniture once every few years, and even then only a few items - refurnishing a whole room or a house happens maybe once a decade.