Love the hard wood floors, and your sofas, chairs and rug! - my thoughts are to move the desk/chair off the stone wall and onto the wall across from the front door if you need it in the room...i'd consider a white & glass coffee table so you pick up the design in the rug, and with the glass you can still see it but the white would look light/clean/modern. You can then pop color..with grey i think yellow can look good / also rusty red or a coppery orange - or dark brown. Lastly, i'd consider painting out the stone walls...not sure what color... you could go: same color as other walls, or an iradescent white or just off white to pick up some light...you could also see about hanging a mirror or something possibly from cool hooks from the ceiling if you dont want to mess up the stone - a mirror could look really great with silver trim maybe - hope some of these ideas help!!