Deep gray and all the other accents in silvery old wood and cream. This will add drama, allow the other elements to bring ion light and set off the concrete wall as a true feature. If you want light instead of drama, then go for a very pale beige stone. It will echo stone colours in both the concrete and rocks...

Now for Mr 16 months... I really can't decide. His room is going to be on the cold side of the house, with not so much sun so I want it to get that cozy sort of feeling when you come into it. I was thinking yellow or orange curtains? But then I don't know what colour to do the walls. These are some fabrics I like:

We are planning to use a dark taupe on one side of the lounge (left wall as seen in plan), and the same dark taupe in each of the bedrooms (1 side only, wall behind bed). Is this a good idea or would u prefer using a diff colour for bedrooms? Thanks

I was about to say grey until I read the last line. What about a light brown carpet?