Sadly the firebox was too shallow for us to be able to put a proper fireback in without building out the front, which we were reluctant to do as we don't want to reduce the amount of space in the room. We considered a gas fire, small stove or inset stove but for all these options either the firebox was too small or the flue was unsuitable. We had decided on an electric fire, but couldn't really find one we liked, particularly in a sensible price bracket. Also, electricity is the expensive heating choice in Ireland.
Finally, we have a solution. Whilst shopping online for something else, Brian came across a nice, sensibly priced cast iron fireplace that fitted the firebox perfectly. He popped it in place one evening in about an hour and it has performed really well and I think really suits the room.