I took my wee one back to Europe when she was 9 weeks old. We were in business on CX and the crew were really lovely. I didn't like the bassinet as I couldn't see the baby in it if I was lying down so she lay diagonally in the seat next to me which fitted her perfectly (we had bought her a seat but I think that one is the last one they are likely to give out so you may be lucky). Almost all of the passengers on my deck had children of varying ages so we didn't really disturb anyone. I didn't know about car seats on planes by that point but didn't need it. She was feeding so regularly that I wasn't going to get that much sleep anyway.
We went back too Europe again when she was about 9 months old but this time in economy on CX. Again, exceptional crew who were so helpful. At the back of the plane, there is one area where the 3 seats by the window become 2. We got the first set of seats that were a 2 but it meant we had a bit of extra space by the window as well as the seat pockets of 3 seats in front of us. This was great for putting bottles/toys etc in so you weren't constantly having to get up and get stuff out of the overhead cabin. We did take the car seat on this trip which was a godsend as she was only just able to sit up properly and it meant I didn't have to hold her the whole time. It also raised her up a bit higher so she could see the TV screen (although she couldn't listen to it).
The great thing about Hong Kong airport is that if you take your stroller to the door at the other end, by the time you get to Hong Kong, it is waiting for you by the aircraft door. This is not the case with other airports (especially UK airports) where you have to collect it from the baggage carousel which is invariably 300 miles away from where the aircraft is.
A friend of mine with 2 wee ones travelled back on her own with both of them and their car seats. She said she just asked the airline for special assistance beforehand and they helped her through everything.
We took my daughter back again when she was 18 months old. Again economy but there wasn't much point in spending to sit up front as she was running up and down the aisles for most of the flight.
Coming through the airport at London Gatwick was so horrendous that I still need sedating just thinking about it

- I spent 2 hours arguing with a horrid little man with a chip on his shoulder who refused to let me take anything on the plane for my child (for whom we had bought a seat) other than her car seat. No bottles, no food, no toys. Hey, it's only a 13 hour flight plus transit time at either end, why on earth would she want any kind of food or entertainment. This, I may add, was not for security reasons, it was just because he was a moron.
From my experience, I would say CX must be one of the most baby-friendly airlines regardless of which class you fly in and Hong Kong is definitely the most baby-friendly airport I have been through.