Where should I put my radiator?

ThisIsWeird

JadeHighland said:

ThisIsWeird said:

JadeHighland said:

Thanks. Added picture in the OP

And size and type of current rad. Photo?

Does the rad heat up well - warm the room nicely?

Anyhoo, a couple of column rads could fit here, I'd have thought, and not be too complex to plumb in:

Or, what's on the wall to your left as you come in that top door?

Current length is about 2m and goes across the entire bay of the window. Heating up, it does a decent job but I only say decent because our windows are very ill fitted. I think once we get those replaced, it will be more than fine. I also remember when we had the old boiled with no thermostat, the room would get quite hot (the entire house would just keep getting hotter to like 28 degrees). The left wall in the hallway and near the stairs, there is a radiator. 

The old boiler would likely have been chugging out 85+ oC water, and the rads would have been piping!
Your current boiler is almost certainly a condensing type, and more likely around 70oC, so the rad will be outputting less. 
You say there is a second rad in that room, against the stairwell wall?
Tbh, I think you'd best have a plumber advise you, as they will be able to provide the best alternatives, also taking into account ease of plumbing.
You probably don't want a rad behind the sofa, but it all depends on the gap you can provide. It should still connect most of its heat upwards, to circulate around the room, but you don't want your sofa affected. 
With your previous boiler, a sofa would have had a tough time, but probably not so much given the lower current temps.
If a column rad(s) would struggle to provide the same heat output on their own, there's even the option of fitting a low rad in place of the existing, to maintain the overall output level for the room - eg a 1' high jobbie, coupled with the column rad.