The photo above, captioned "Southampton" looks perfect for your home! On the inside, consider drapery panels with a grommet header, hung high on the wall. Would keep it contemporary but add a soft touch (very helpful on cold or cloudy days).

If you don't want to make the wall itself straight, maybe consider playing with some deep shelves ABOVE the TV, that could go from the diagonal wall to the straight line where you want to put the TV. Then behind the TV you could have a vertical panel of the same colour/material of the shelves (or matching the colour of the wall) to connect the TV stand to the first shelf and hide the awkward wall. To avoid having empty space right beside the door you could put a narrow shelving unit (with a back panel, not an open one) between the TV stand/panel and the straight wall (or beside it if it's short) that goes from floor to first shelf, again I'm imagining same colour/material of the rest so it binds seamlessly rather than looking like patchwork to fill the space. It's a little complicated to explain but I hope it makes sense!

Looking for inspiration to decide what to hang on these lovely cream paneled walls in the hall and the living room. Not mirrors because there are already enough in the house. Thanks

Love your room, we have Farrow & Ball Mizzle, its a light greyish green with Little Green Clay Mid which is really a soft white with a tiny hint of grey on skirtings and doors. That would leave you free to go for a stronger colour on the back alcove walls without 'darking' the room much. The upper sample green on your wall should match well with these colours. Colour would be easily brought (and changed) in with rug, cushions etc, HTHs