I do this trip about 9 or 10 times a year in Y, C and F depending on the time of year, how much money I am making and award availability. At present Y usually has about 100 empty seats and on my last flight I had 3 to myself. Does n't seem much value paying for C in those circumstances.
The period you are flying is almost certain to mean Y is full and C and F will likely be as well so an op-up or stand by upgrade is highly unlikely and I think ROP Gold will get these first if there were any. For this period I would advise you to book now.
I have no trouble sleeping in Y and will sleep about 7 hours of the flight. For this reason I always fly the night flights. After the return flight I can be at work by 08:30. To me the day flight either way means a day lost. I am not troubled by jet lag flying West and on the return so long as I stay awake until 10pm I am fine.
If flying solo I would book an aisle seat in the middle D or G as you only have to get up for one person. and no one has to move for you. Contrary to most advice I prefer to be near the galley, that way I am aware when they start preparing breakfast and I go and use the bathroom before they have queues. Try not to get an aisle seat near the toilets as you will be disturbed by inconsiderate people talking and/or leaning on your seat as they queue for the toilet.
If going to Heathrow by car either get there very early (17:00 latest) or about 19:30 to 20:00. I once left home an hour earlier and got to the airport about 10 minutes earlier than normal. Such is the M25/M4. For this reason I fly out Thursday not Friday. I return Sunday evening So I lose the least days away from my UK business.
If you are leaving a car at the airport book the valet parking, this saves about 30-40 minutes at each end. Meteor do this at little more cost than the on-site business parking.