I love the aqua blue and browns you have for this room. Given your furnishings, they have a mid century modern style which you could capitalize on. (see the bedside table in this image is like yours)You can easily create a base of browns and a cream or patterned rug and then find some bedlinens in the cyan/aqua colourhttps://www.houzz.com/products/organic-ironwork-duvet-cover-prvw-vr~501905 and then find a fabric that matches your duvet cover to cover the chair...It would be nice if you could either spray paint the bed (which I think is black metal) a silver metallic colour to lessen a harsh line. I would also remove the shiny sheer drape you have in front of the curtains. Why are they there? You seem to have venetian blinds as well.Can you hang the mirror up higher or is it part of the dresser? The base should be about 20cm from the top of the dresser to create some height to the room. I would also lower or even remove the painting in the room as it is too high...For the other furniture, I would rather work on some simple basics and then we can adjust them around. I think your bed is in the only place it can be....

It's really a matter of personal taste, but I think I'd add a blue. Generous but simple drapes in linen, or for a contrasting texture something with a sheen would look luxurious with a quality rod .

It would look odd with just a curtain rod across the void. You could get a pelmet made, or fill the void above the curtain with a shelf or cupboards though this will involve a little disruption. I would avoid plastering too as it is a messy process that takes more than one day and needs painting too. You may still want blinds on the windows for light control but soften the whole look with side drapes as you asked for. Shutters could also work either way but they are pricey.

Cant wait to see more!