is the one behind your radiator a double convector rad ?
you may find it doesnt need to be as big if its not currently one of the above.
We did have a massive single rad in our place
we replaced it with a much much smaller under window double convector and Its in a much better location so the room heats up much better. the old one was behind the door so the door didnt even open propper.
Id always keep the radiator though – what about in the mornings when you get up for work , nice to be able to sit on the sofa and see the news without freezing your arse off.
Put a TRV on it though so it kicks to off when the fire has got the room to temp. Means the rest of the house will heat up as well as the lounge , although my eco fan is doing a sterling job of getting the room warm in an hour and the house warm in a couple of hours.
my heating only runs in the morning – might adjust that once it gets really cold though so the house is moderately warm for me getting in with numb toes