You need heated seats in an 8 as I find the heater pretty hopeless. I think it's better for the passenger, but the driver gets almost no heat.
Try closing the vents behind the radio (there are 3) and make sure the one in the drivers footwell is open. It isn't obvious and you need to use a torch to find it: once you have "learnt: where it is then you won't need a torch!!
I find having just the centre upper vent and drivers footwell one open works well, all the others shut and as long as the fan is on and the heat control fully open. Doesn't do much until the engine has warmed up to 60C plus, about a mile.
