The dark floor would be lovely imo, but I would put cushions in bright colours, even duck egg blue and other almost caribbean shades on the sofa or any dark upholstered chairs if you have them (but no yellow). I would leave the bannister dark, not just because white paint would look grubby immediately, but because a dark bannister would be nice.
Thank you very much, all of you. I'll pop up and see the floor today and see if DH likes it as much as I do. I've been looking for months, since October, so hopefully get some today while it's on offer.