Poor DS (nearly 12) has had the same bedroom since he was two - same curtains, furniture, plain cream coloured walls. He is not complaining but I know we must do something soon 
Limited budget so we're not talking major new furniture, but perhaps a few things to make the room more grown up. He has a reasonable IKEA desk (not babyish), bookshelves and chest of drawers.
I was thinking of painting one wall a dark colour (navy blue?) and leaving the others plain. Curtains def need changing as they have spacemen on them.
How can I make the room more grown up and suitable for a soon-to-be teenage boy, without spending loads or going OTT? He's sporty but not excessively into football, loves science, geography, geology.
Any ideas or inspiration most gratefully received - I just don't know where to start.