Your range does drop in winter compared to summer for a variety of reasons, which includes using the heating (also windy weather, rain with wetter roads, etc). As has been said, the heat pump is more efficient than just the standard resistive heating, particularly on longer journeys, although I'd struggle to define how long is "longer"
If you can, it's worthwhile using the car timer to warm up the car while it's still plugged in. Then all it needs to do from the battery is keep the car warm rather than heat it up in the first place, which is the bit that uses most power. Same applies in summer for cooling. You can either trigger it yourself from the app or set up one of the "departure times" in the car. I am on Octopus Go for electricity, so set two departure times in winter. One to charge the battery on cheap electric between 00.30 and 04.30, the other to heat up the car just before I need to go to work.
I am one of the few people who actually use their garage to keep the car in, it's much cooler in summer and warmer in winter. And it means I stay dry when I'm unloading the shopping!
I have the heat pump and winter pack, so have heated seats. But generally that just means I have the car temp set to 20 or 21 as well as a cosy bum. I made the decision that although I value efficiency, I also wanted a car that was comfortable. That doesn't include seeing my breath in front of me with the windows steaming up whenever I'm driving because it happens to be frosty outside.