Hello Ethan, thanks for your reply, I really appreciate, as I'm really unsure how to proceed.
Unfourtunately those metal cupboards are fixed. Moving the TV would be tricky - its on a table the same size as my studio desk (140cm) - maybe I could try that though... Would it still work as a set up if the metal cupboards stayed in place, and I had my studio desk against the right wall (that is, with the skylight to my left, and metal cupboards to my right?).
I also had the studio desk up paralell against the wall in the top left (see diagram "roomwall" attached). I did a REW test in both that position, and with the position facing the corner. I attach the graph of the frequency as well -- not sure how to interpret it, but seems the corner has much more pronounced peaks and nulls... the green in the graph is facing the corner, the red in the graph is facing the wall.
Other option I have is to move to another small room which is 250cm by 270 cm room (which has 65cm off the 270 cm width with some fixed wall-to-ceiling shelves), room height 235 cm. Perhaps a little too close to a cube which is not recommended? But if this is a better option (with some treatment) than the odd-shaped room, I can go with that ...
I made a REW frequency test for various positions, from corner to facing the wall. The best results came with the speakers right up against the wall. Thinking now about treatment for the room, if the speakers are right up against the wall, there does not seem to be any room for corner bass traps. If I bring the speakers away from the wall (see diagram) to allow room for bass traps in the corners behind them, it feels like I have a wall on my left, but a big huge empty space on my right. I wonder if that is partly the reason for better results with the speakers right up against the wall as the fireplace then creates some symmetry ... or, if I bring the speakers away from the wall, if I put a standing panel to my right, would this offset the fact that there is no wall beyond it?