We have a similar sized room for Bratling. I put her bed on long legs, and the chest of drawers under it. She sleeps at my chest height now, and it's a lot easier to put her into when she's asleep and you don't want to knacker your back by carrying her up and dropping her in. The step ladder doubles as clothes rack and book shelf!

This leaves a little space under the bed for a play area (her trampoline fits nicely, but she pulls it out to use), space to get to the window (yours open inwards? Strange windows....) with a book shelf where your fireplace would be,a tall shelf unit and small bedside table behind the bed, shelves on the wall, she has room to play, a whole wall free for chalking and pinboard, and plenty of wall space for more shelves should we feel so inclined.

LTS