I think white walls would make the jarrah a feature, maybe antique white

I agree, your slate floor is actually a really nice slate. A little tip when choosing paint colours is to get the sample pots and paint a really large piece of cardboard. The colour blocking just highlights the interesting features of the house. I know the charcoal will work and the Grand piano is just a warmer white. You will need a warmer white to complete the slate. Other suitable whites will be China white and maybe Whisper white. Too white will not work with slate. My father and brother are painters and I choose the colours, still colours are a very personal thing, that's why I'm suggesting the cardboard idea. Hope this helps.

I'm going to be tricky and recommend staying within the cool palette. Sometimes when you mix warm and cool colours, even if they're neutrals, they can bounce off each other strangely and look bad. Lexicon is pure white with only a touch of black added (no other pigments) and your 'Black White' cupboards may well be the same. Paint some areas with a sample pot first if you're feeling hesitant, but I do think the colour consultant was a great idea. Good luck!

Dulux gentle calm half would look lovely against your bedding choice. Would you also consider painting the window wall a dark feature green? It would play nicely with the lighter gentle calm wall colour for the other walls in the room. One thing to consider is your dressing table is a warmer antique white, whereas your bedframe is a stark white. Would it be possible to paint one or the other so they don’t clash? I would also consider adding a longer curtain rod so the curtains are against the wall corners when fully open. And if there is room I would have the dressing table flush against the right wall, rather than on an angle. Love the bedding colours though and how they tie into the curtains nicely. I agree with you that the yellowy cream wall colour doesn’t quite compliment your other design choices. Good luck!