The most essential decision for this layout is position of the desk. It is a small room with lower ceiling and there is one door almost in each facade. So it is a good idea for a person working on the table to see both outside and entrance while working.
Another important thing is about sofa. I think the position is the best and there is no other option. So under these circumstances, I had to chose a smaller desk than your example.
You are asking for ready made furnitures and I prepare two options for you because I am not sure about your style. Plus, it is okay to use existing sofa however, Wassily Chair will be too much for this room.
Finally, please chose one of these furniture lists prepared as a mood board.