the existing yellow could be the worst problem - yellow is about the hardest colour to get right.
In the shop and working from swatches it is easy to get a yellow that tends towards the green end of the spectrum, this will make a room strangely gloomy - there is something to do with scale here yellows seem to change when the area covered gets larger.
I would always over compensate towards the orange end of the spectrum, it glows, is warmer and generaly more cheerful.
i should add that I am talking about very subtle hue differences here, the difference is only just perceptable on a small swatch - line up a whole load of yellows and try to order them from greenest to orangest to see what I mean. also be careful of choosing a colour that is tonaly dark, even yellows vary in how dull they are. a good trick here is to squint and try not to focus while you look at a selection, you will see the tonal values more clearly.
I agree with feldri that a picture rail would brighten things up signifigantly, also the line has the effect of visually widening the room, adding a chair rail with two colours can increase this effect (lighter colour to the top).
however i disagree with the choice of satin paint, I would use a good bright white matt emulsion above the dado and on the ceiling - the slight reflection that you get from satin paint is the surface bouncing light back into the room - and probably onto a darker colour. this is good if you have a window and want to spread the light around - but in your case you want the most white ambient light that you can get, so to have the ceiling glow rather than reflect would be better.
to see what i mean imagine covering the ceiling with a mirror - you would have all of the light reflected away onto the walls, so much so you could see the reflection, but a very dark ceiling.
another good trick is to use uplighters rather than a ceiling pendant light.