Take your keyboard to the shop and try some PC speakers and see if you like the sound. You'll need to run them from the stereo headphone out - not the main L + R outs. You'll probably need to use an adaptor - the headphone out is a 1/4 inch stereo jack (AFAIK) and PC speakers are usually a stereo mini jack.
If it's just for home they'll be fine. I've used little powered PC speakers many times with stage pianos and synths to get in a bit of practise between gigs or work out a new arrangement with a singer (or instrumentalist). Cheap, quick to set up, not too loud for a flat.