Here are images of my first floor and basement. I recently added a second floor and expanded it, but am still unsure what theme would look good with what I currently have going on. Any ideas?
You could turn your basement into an outdoors themed room. There's so much greenery furniture out there now; the greenhouse box, flower beds, swinging chairs and you put your own flowers in there too like golden roses. Maddie's RV has heaps of outdoor stuff. The natural set goes so nicely with that wallpaper and flooring you've got!
As for upstairs, my upstairs is my bedroom. The Kiki & Lala stuff seems to go nicely with the mermaid set in my opinion, so you cold much some items together from those two sets ~