A big screen can be nice, but it makes you feel disconnected from the road, bizarrely, which I couldn't get on with.
Do you have handlebar muffs? Or heated grips? They can make all the difference.
I have a waistcoat that takes 4xAA batteries and heats using two elements. It drains the batteries in about 10 minutes but I used to wear it on my 110 mile rides to go home at the weekends on the C90 in winter, to give me a 10 minute boost of heat when I was really desperate.