The ceiling is gorgeous. Everything else needs changing but I assume that's the seller's stuff (and that the seller is a 'developer')? What's the age of the house because that ceiling looks late mid century but those doors look like inappropriate 'modern' additions? Also, is this the main sitting room in the house or a large entrance hall? Because they should be treated differently.
I think with that ceiling you have three options depending on your personal taste.
Firstly, paint the walls a white with an undertone that goes with the ceiling (and floor if keeping), then keep the rest of the room toning neutrals but increase the variety of textures and shapes so include e.g. a banana shaped boucle sofa or a tan leather sofa or a circular coffee table.
Secondly, lean into the rich colours of the ceiling and colour drench the room (including the floor and furniture) in pink/burgundy tones.
Thirdly, go for green walls, cover the floor with a selection of large, vintage persian rugs, and have a more slouchy curvy sofa (a togo sectional sofa would be fab in this space).
More general comments: what's the point of the niche under the stairs, would it be better to include that in the understairs cupboard and have a wall there that can be used for bookcases/shelves/art? Or is that an interesting original feature? Agree that changing the venetian blinds to curtains would help warm up the space as well. But I think when you start moving your own stuff in that will warm it up a lot. Mid century houses have unfussy furniture but they did have stuff, this was the era of the shelving system after all.