Looks like a small space. Gray lest her with chrome legs sofa 2 sestertius. Think scale. Place sofa to look at view or a TV.? Not sure what room is used for? Get 2 swivel chairs in a fabric print. Yellow and gray works. No rug over rug. Never lays right. A black small 20" round metal coffee table. Lamps in stainless with white shades with end tables buy sofa. If TV a long low media in black or white. Ikea, go there for all your needs. Good price, and some great art. There is the London underground 40" for over sofa. Hang all art 6-7" above top of furn. Keep it low, clean sleek lines. Not too big. On windows gray and white print panels on ends of windows only. Ikea. Hang on a black rod. They should touch the floor. Accessories on coffee and other tables. Tall pots in black, grey, yellow. Teal, or blue green works with gray also. Keep sofa always a solid color and chairs can be a contemporary design. Use only one accent color in a small room. Carry same accents to other rooms to tie together.

Floor to ceiling, and ideally on a ceiling track. Sheer unpatterned curtains have stayed relevant for a long time now and they can be complemented with a blockout curtain. Provided the ceiling track / curtain system can handle a bit of weight, you can always change the curtain material. Make sure the system itself looks "minimalist".

I've just been looking at your colours, I think the Dulux Dieskau would work the best with the other colours you have to work with, choosing colours is such a personal thing and I know it can be really hard to choose and hope you make the correct choice. Oskuee is right, a paint job can look terrible half way through so you need to make sure you finish to get the proper look of colour. But the biggest thing to remember is it's only paint and it's the cheapest thing to change so if your not happy with the colour you choose you can always try something else. Happy redecorating :)

re the floor, what about garage matting tiles, as in photo attached, but lay them in a groovier pattern, perhaps a chevron or 60's pattern, if leaning towards MCM. It may not be any dearer than the cost after getting a tiler in, if laying tiles? Also, you can take them out to clean them if need to and change the look whenever you feel the need!