Wallpaper is one of the easiest ways to change the atmosphere without replacing all the furniture. I was helping with a bedroom where the walls were completely plain, and one patterned wall made a huge difference. We looked at different styles here https://costacover.com/collect....ions/teenager-wallpa eventually chose something expressive but not overly childish. The neutral furniture works with it really well, and changing the bedding or posters later should still be easy.