Shelia, don't forget the cumulative effect of two major surgeries in a short space of time. I think it's understandable that you feel as if your second knee isn't stable or strong yet. It only has the support of a knee that is still recovering from its own surgery.
Keep using the walker as long as you feel safer with it, and don't try to rush into using a cane yet. It's a big step to go from using the walker to using only one cane. I didn't have a walker, but I needed to use two crutches for at least a month, before I started using only one. It's much better to use a walker for longer than to risk a fall.
Yes, a whole flight of stairs can be scary, but just take your time, and rely on your husband being a step or two ahead of you.
Oh yes, and don't compare your two knees. Knee number two is on its own journey. It knows what it's doing. It's going to be just as good as your first knee, but it will do it on its own time frame.