Thats a bueatiful room. I sure it echoes like crazy being empty. Some carpets and others sound deading materials would work. Lots of plans for simple cheal acoustic baffles online.
I have an upstairs room alos and both me and my wife love it . I can do what I want and she doesn't have to worry about a mess ( in her eyes a mess is and empty coffee cup )
Also building my model RR up there. Good therapy hobby.