Thanks for all the replies! The Brume 1/4 looks good, they told me it was an older colour now but could still mix it up. I found White Duck 1/4 which looks almost the same, it has just a touch more yellow in it rather than green so apparently is warmer, but looks grey/stone when compared to more yellow Hog Bristle 1/4 on the test boards I've done. I wonder if both colours are too light - they have barely any contrast to ceiling, but I'm only going for neutral/off white effectively and the unit can be dark so I worry that going 1/2 strength might make it too dark?
Also, for the trim colour, I was tossing up going with either white or a half/full strength colour to match whatever I pick for the walls, but was recommended that I get the gloss done in the exact same colour as walls? I thought white might make it more versatile for a quick repaint if needed later on, cos it's the trim that's the more fiddly/costly element... What do you think? Looking at white blinds if that helps.
And finally, prefs for paint gloss type? Walls - I was quoted 'Matt', but 'low sheen' seems to be better option? And for trim, full or semi-gloss?