Marble would still work well in all those areas - luxurious and dramatic! A couple of points to take care with: - Take care if you're option for high gloss, as they can be slippery when wet - If you're opting for a very "white" marble (Carrara or some such), be prepared for it to show every dirty mark and need regular cleaning. If your lifestye can cope with this great - if you have three labrodors and live in a pair of Hunter wellies, I'd urge caution....

You can use it on walls, ceiling and skirting if you like, though I tend to prefer a pure white for the skirting ( it's cheaper to buy as well) as its a nice crisp finish.

OMG it's like going from a panic attack to a leisurely stroll through some stately gardens on a sunny day. Marvellous.

Just a cheap but effective solution. We also have a kitchen / diner in an L-shape with a small lounge area attached.................all open plan. We have one large radiator that was heating it. Firstly, I notice that you have no curtains on the window in the middle. All the curtains ( including the window ) should be thermal backed and as thick as you can get to stop the heat going out of the glass. Secondly, the little radiator in the middle of the double doors doesn't look like it is large enough to have an adequate heat output for the size of the room, so I would change that. There are charts on line to work out the size you need, or if you enquire at any decent plumbing merchants, they'll work it out for you. Adding a good depth window sill to under the window will help prevent heat loss up and out of the window too. We bought a ceramic radiator to plug in, in the conservatory as a back up to our larger radiator and it works a treat! Really slimline too. However, the biggest saving on the heat loss is our curtains, which are really, really thick, make sure they cover the sill.