This looks like a lovely sized room. I’m sure this layout would work well but do you really need a bath in there? I would suggest a really fabulous shower and use any room saved for additional storage ( Your plumber could even run a hot water pipe from the central heating system through a tall cupboard which will keep your towels snuggly and warm). I would leave the loo where it is. then put the cupboard and double vanities where the bath is (60cm cupboard and 120 double vanity) and a long walk-in shower along the wall where you currently have the sink.

One little addition which I have in my bathroom is a motion activated light situated low down near the loo (mine is actually underneath a wall hung loo). At night any bathroom trips have a little bit of ambient light to get you where you need to be without a glaring main light to wake you up. Good luck with your project. Im sure it will be fabulous

Agree with gb regards bath and lighting 

Would be tempted to create a dressing room / walk in wardrobe where velux windows are, as would make bedroom feel more cosy 
Velux windows are also noisy when it rains ἲ7

Thank you both. I have heard velux can be noisy so we will consider a dressing area to make it cosier. Although we really need lots and lots of storage! As we are losing the attic space and we stored a fair bit in it in our old house. We did consider a walk in shower but I am so keen to have a bath. I will have a think though. I have been told we need to lose 25cm off the width up there (which will probably come off bathroom) due to a chimney stack not being accounted for. Love the idea of motion sensor light for nightime loo trips! Thanks