Is there something in the room you want reflected back that you love looking at? If not, why don't you find a nice piece of art work for the fireplace so you have something to enjoy rather than looking back at your other wall?

I love the look of Tand G as the real thing or the 'James Hardie' NZ groove panels..........but also want my ensuite to look opulent. I am not having tiling anywhere in this room, which would be the easiest solution. Hence my dilemma..... I already have chosen the white 'tile look' acrylic walls with a feature 'marble' (narrow) panel in the shower alcove enclosure from the 'Atlantis' range. The alcove covers the complete width of the bathroom so is a feature in itself. I wanted to bring the 'marble 'feature' into the room if I could to enhance the opulence. The marbling is minimal veining on a white background so not too dramatic a feature. The obvious area is to use a matching 'marble' vanity top and/or a splash back (especially if have a china vanity top, which is the more likely due to cost). Where should the splashback end at the sides? I thought about taking the 'marble' splashback above the mirror to the ceiling thus creating a similar panel feature to that in the shower albeit wider but don't know how much wider it should be than the vanity. Also What then to do on the rest of the wall(s)? Just painted gib? If I used T& G or groove panelling I would want it to reach the ceiling. So do I put T&G on on all walls? The vanity wall has approx 1000mm 'strips' of full wall either side and the strips below the vanity and above mirror if only a splashback is incorporated. The opposite wall is almost taken up by window, radiator below, btw toilet and towel rail, leaving little wall to 'feature' and then the remaining wall is narrow (only 1100 left after door). These remaining walls could just be left as painted gib of course as really cannot afford to take the 'marble' panelling anywhere else in the room nor think where else it would feature best. 'Marble' Flooring is a possibility but it would need to be vinyl not porcelain tiles. Having written all this down I think I have talked myself out of T&G on any of the walls as the narrow room would become too busy and bitty but am still interested in what others think.

Are there rules of thumb about size and type?

Your client putting trust in you was the right decision! amazing transformations! Love the natural light in particular as thats a great spot for a post gym pump flex for a good selfie!