A good nights sleep comes from a really good mattress. One that is suitable for your body. The style of bed would always depend on ones personal taste J Design Group, Modern Interior Design Firm in Miami, Florida. http://www.JDesignGroup.com

I've just cobbled together a quick plan for you and then on re-reading OnePlan's suggestion above I realise its the same thing so apologies for that. Wasnt trying to copy. If you have more accurate dimensions I'll happily put together something a bit more accurate. With this plan you lose a bit of space from the front room and the bedroom but you turn the flat into a 2 bed, great for when you come to resell. To get light into the bedroom you could have a frosted glass panel in place of the existing window and as long as there are rooflights above the kitchen then the bedroom will get some light but its not going to be a great sunny room.

At the risk of contradicting previous advice, warm colours suit a dark and north facing room much better. If you are set on blue, then I would go with a rich dark blue - Stiffkey has been mentioned and it is an awesome shade. You could then do the paintwork to co-ordinate with the wardrobes to tie them in, and use patterned or textured soft furnishings as a bridge between the two colours. Embracing the fact that the room is dark rather than fighting it gives you the chance to make it a cosy nest, with plenty of texture to break up big blocks of colour and make it even more warm. A blackout blind and soft full patterned drapes will get around the radiator under the window issue and add more interest. I see you have metallic lamps - more metallics and and clever use of mirrors will help reflect any light you do have in the day, and your low level lamps will help make it warm and intimate at night with reading light as a bonus. My five pennys worth...

Budget permitting, matching the curtains and bed spread and adding a pair of matching and/or coordinated pillow shams along with a coordinating solid color bed skirt could make the room more formal/decorated. Something interesting above the headboard, preferably something that reflects your family's interest -- art or something on shelving, preferably modern artsy shelving -- or even a pair of swing arm wall lamps above the headboard could be all the wall decoration you need. Choose something that would add your favorite colors to the room but, unless and until you find something you truly like, leave the walls blank. Pressed metal wall art might be something to consider. http://ep.yimg.com/ay/newportantiques4-shop/mountain-scene-burnished-metal-wall-art-10.gif http://www.interiortaste.com/wp-content/uploads/2012/10/abstract-metal-wall-art.jpg You likely need more drawers for storage. Instead of bedside tables, consider a pair of wider cabinets or dressers with drawers that can serve the same purpose. You might also consider a pair of his/her file cabinets for bedside tables -- everyone has documents to file away or they could just be used for clothes. I like the second one on this page. http://office-turn.com/solid-wood-four-drawer-file-cabinets/ http://office-turn.com/wp-content/uploads/2011/10/Modern-Shaker-Solid-Wood-4-Drawers-Lateral-File-Cabinet.jpg You don't mention how high or wide the radiator is. It may be you cannot put anything above one that provides heat but see if you could add a corner cabinet or see if the white chest of drawers could fit beside the radiator or would that impede walking around the bed. Alternately, across from the bed you might consider adding shallow shelving to the wall above the radiator and/or beside it -- perhaps something with a drop down shelf/desk. http://www.eastsidehomelink.com/wp-content/uploads/2014/11/Wall-Mounted-Desks-Fold-down-Desk-with-Drawers.jpg