If you are in eco mode you should still be able to heat the cabin, you shouldn't go with out heating, most EV cars systems do limit the heat it can go to, but not shut it off.
Some of the heat is still a by product of the battery and the car uses that.
Obviously the 4 with a heat pump isn't available here, but strangely is in Spain, which is basically because the EU left hand drive model is pretty standard across the EU and Germany etc do get far colder winters than the UK.
I watched a you tube video of an EV owner in Finland comparing the same car with and without a heat pump and the difference in efficiency was negligible, it was minus 20 and the boy was still getting 2.8 and that was with studded tyres too.
He did actually add that his cars efficiency seemed to improve after he had it for 4, 5 months. Almost like and Ice car when you ran them in