Flooring - carpet
Colors - soothing (earth tones)
Lighting - soft
Overall, you want to create a warm, cozy, inviting space so they won't say "office" right away. You should also stage it as a bedroom so they can see that it fits the furniture and can be practical despite being a little quirky. You might also consider playing up the funkiness, by decorating to stay with a funky feel - they might just love it!