The word translated as "upper room" means "higher floor" literally, "high ground".
The word translated as "furnished" means "spread-out". The word, however, doesn't appear in the Perseus Greek in this form but in a version with a prefix. However, all other Biblical uses of this word, both Old and New Testament translate it as some form of "spread." It may have been used like we use a big "spread" to describe a dinner table with lots of food, but this seems unlikely. It probably just described a room taking up the entire floor.