Avoid themes as he will change very soon. I did both DSs around this time and went for bold and bright but plain bedding. One bedroom wall is dark and the rest light. They seem to have stood the test of time.
I get all my teenage DS' bedding from BHS. It's bright and garish enough for him and decent quality.
We have this: http://m.bhs.co.uk/mt/www.bhs.co.uk/en/bhuk/product/home-lighting-2253424/bedding-1020702/bedding-sets-1020703/no-jumping-on-the-bed-2151284?refinements=category~[471665|471194]&bi=81&ps=40
(Sorry can't link from phone)
They also have checks and stripes if you want something plainer.