It depends how bright you'd like to go? Natural tones are very popular at the moment. I'm thinking something you could swap out if you get tired of it. Brighter cushions maybe and a much brighter rug on top of yours in a smaller size. You could leave everything and put all your effort into brightening up your built in bookcases either side. Even your book spines are muted. Start small with a few brighter books and see if you like it first. You have one accent orange cushion maybe carry on with that idea. Even a brightly coloured plant or flowers on the table would lift it.

Paint the dining area wall? You don't show the other side of the space but different shades or tones would differentiate the areas. As Isla says, if you like the orange, consider curtains that would pick that up as well as spots of colour on those lovely shelves. Look at a colour wheel for inspo on taking the kitchen blue through to the sitting room orange??

Thank you for these suggestions, I was considering going really bold and opting for a darker colour for the living space, something like this!

That would certainly do the job in terms of differentiating it! I assume the living room is light enough to handle this? If you're thinking of it at this time of year that probably answers the question!

The bold colour looks fab. Painting the skirtings and ceiling looks great. I would wrap out your second sofa for 2 armchairs to improve the flow between the rooms.