Insulating external door in old house

I have just removed the ugly storm porch (single glazed aluminium) in the course of a refurbishment of my 100 year old house. I know I'm taking a chance in terms of heat loss but it was really brutal to look at. The porch is recessed from the hall door - approx 2 feet. Apart from insulation strips/brush strips for bottom of the hall door, has anyone extra hints on how to minimise cold air coming through??

Many thanks

How about hanging some kind of curtain inside the door that you could close over in evening / night.
They use a kind of heavy leather curtain in Switzerland and the like in winter time I have been told.
best of luck