Would agree with the majority of posts, but something BA are not keen on being reminded on is that they reduced the seat pitch about 10 years ago, from 32-34" to 31" (some seats have even less!!)... fitted slim line seats and reduced the thigh support, foot rest is useless and be aware of any video box under the seat, not sure if they were removed when AVOD fitted.
consider purchasing a real pillow for a fiver, grab a window seat and lean against it. chuck it on arrival and buy another one if you can't be bothered to carry it with you. Aisle seats....??? Well there is nothing worse than managing to fall asleep when the person next to you or by the window wants to either stretch their legs or visit the loo etc. Good luck... enjoy HK.