That was rather unkind of them to not tell you this earlier, but I suppose they feel like there is plenty of time between now and your surgery to drop these little things on you. (sarcasm here) This happens sometimes and it can throw your plans for a loop. You'll be making a lot of these little adjustments as you go through the process of preparing for surgery and recovery.
Figure out a good place in your house to create a "recovery nest" for yourself. Ideally it would be a spot where you can spend the day (and even better if you can sleep there too at night), close to the kitchen and a bathroom, and where you must do minimal or no stairs. You'll need a comfortable couch or recliner where you can rest with your leg elevated and well iced. You'll probably want a television and other things to occupy your time when you're awake. You really won't be wanting to attempt those 18 stairs to the upper floor on a regular basis for a while when you come home from the hospital. Although you might be able to do it, it will tire you out so much that it's not worth it.
If there is not a bathroom on the main living area, you could use a bedroom upstairs. But you'll want to set up a small refrigerator or cooler for someone to stock up daily with your snacks and ice. With a little planning, you can make this work just fine. Remember, it's only temporary and you'll have that wonderful new hip for many years to come.