Might be better to try a different light bulb first, go for a blue/daylight bulb, will make your whites brighter. Whites, especially in enclosed spaces without any other colors, will tend to appear greyish, if you are looking to brighten the space consider switching the wall color to a very pale pastel instead.

Not at all, consider using a brighter white for the walls such as BM White Dove.

I would actually consider keeping the cream because I think it looks nice, don't think it appears too dark, and may give even more warmth than white to a space with no natural light.