Comfort seats are nearly always standard. The way to tell them apart is that they have a separate headrest which matches the rear seats on an F12 or F13. The sports seats have built in headrests and match the rear seats of the F06. I thought both options had lumbar though. The ones below mention it.
This car has the sport seats and you can see their style really doesn't match the rear seats
https://usedcars.bmw.co.uk/vehicle/2...e-7b32e9b9b4a6
This car has the comfort seat option
https://usedcars.bmw.co.uk/vehicle/2...6-141216aaf2e7
This car has the sports seats front which match the rear seats in an F06:
https://usedcars.bmw.co.uk/vehicle/2...9-93c43fb569fc
Finally here is an F06 with comfort seats front which don't match the rears
https://usedcars.bmw.co.uk/vehicle/2...e-58b8c9c66dd9
This time last year when I was looking for mine I did see there were a lot of M6s for sale in the UK and they stayed around for a long time. By about March or so most had been sold, I think I remember around 20-25 Coupes listed and by March there was about 10. At that time there were still lots that were only a few months old and were 60-80k pounds, now there are none.
As such I'd recommend buying in January. The dealers will have had the car since November probably or even earlier and are thinking it will be there for another 2 or 3 months before it actually sells.
I ended up buying an NZ new one because I really wanted LCI, Comp Pack, Ventilated Seats and the only NZ new Comp Pack came up for sale at the perfect time for me. Very few cars in the UK have Ventilated seats. LCI came out early 2015 so you should be OK there.