Kalle : "In a room of that size there's hardly any real options for monitor replacement. "
That's sort of giving up before starting. I agree the room is far from ideal.
The idea is to have the best setup in mind then adapt it with as little change as possible to the room at hand. Things have to be as symmetrical as possible left to right.
If you're after the best sound, then you might very well decide to have your desk in the middle of the room. Well, not the middle because that's a really bad place. A few feet forward of middle should be pretty good. I'd certainly have my monitors well off the back wall.
With only 7 feet across available, you definitely need absorption on the side walls to reduce the first reflections from the monitors. And you'll be sitting pretty close to the monitors and that is good in a bad room.
Having a floor plan of the room in question with openings like doors and windows would be a great help in looking at options.