if you have business to attend to in LHR, then yes, do flexible meal a per 2 above...great advice. and don't drink too much. it is a short flight and a hang over with business at 10am when your body thinks its 5 sucks.
if not, i would just have the regular mean and watch movies and relax and have a few libations...
just remember the call button since if you do this option, FA's might assume you want to sleep so push the button if you need a re-load.
don't load up on too much wine/booze in the lounge - if wine is your thing. it's poor quality and i think AC has one of the best champagnes in J (and i actually prefer it to many more of the fancy label's - well, what others think is fancy), drappier....i just drink it and perhaps some port and some VS, although not sure if they have any VSOP these days....
note, what they serve on the ground is not the drappier so once in the air, specifically ask for drappier during the first drink run.
i have started to just change into some pajamas i got on some other flights. it actually is much much more comfortable.