It depends on what type and finish you want and if you do the job yourself or pay an electrician.
Recessed lights (eyeball lights or downlighters).. brass or white finish, low voltage, halogen or normal screw in spotlamps. Try Argos or Wickes.
If you fit them yourself, if downstairs, it will mean taking up some floorboards upstairs to put in additional wiring. Depending on the wattage, will any dimmer switch fitted handle it.