Hi. I would try rearranging the furniture slightly. Try the desk on the back wall next to the wardrobe. Swap the chest of drawers and bed around (assuming the door will open, hard to tell from pics!). There's quite a contrast between the blue and cream walls. It looks as if your son has london skyline pillows (or it looks like St Paul's from what I can see!). If so, why not try a slightly urban look? You can get enormous wall murals from around £30. Try the London skyline or maybe a banksy mural or something he's interested in. Unless you can afford made to measure just get the biggest one, centre on the wall and paint the remainder so it acts as a border (depending in the image you may be able to trim the top and bottom so height wise it fits perfectly). If a mural isn't up his street try brick wallpaper and add street signs (you can get cheap vinyl ones if on a budget) or prints of whatever he's interested in. If he likes the blue (is he a chelsea fan?!) , paint the window wall in a soft grey/blue. If he doesn't maybe try navy or charcoal grey. Adding a throw ( a manly one!) and 1/2 cushions on the bed will help. If he likes the street signs idea you can get these or tube stations etc pretty cheaply or just add dark grey ones with a bit of texture.

I agree with playing with the furniture layout, I would also add the colour grey in the form of blinds, bed linen, rug etc as it will compliment the blue beautifully.

I suggest also adding framed prints of various sizes grouped together and sorting out the xbox and tv presentation.

To this end I would place the bed on the wall where the wardrobe is. I would purchase another wardrobe to match what you currently have and place both wardrobes side by side on the wall where the tv is. I would remove the back of one wardrobe so the tv etc is built in and hidden away.Place the chest of drawers where the wardrobe currently is located,

Place the desk where the bed currently is (or thereabouts allowing for walk around room for the bed) and then see where the bedside cabinet will fit. It may not be needed because the chest of drawers will also double as a bedside cabinet with this configuration.

Where the bedside cabinet is located I would purchase a cheap bedroom chair (charity shop) and have it recovered to match the curtains and bed throw.