I will be flying when my girl is nine weeks as well, I would say it should be doable
We found travelling with a baby was easy! We travelled extensively in Europe and Asia from 10 weeks until 9 months and it was brilliant. Since our little one started walking it’s been a nightmare though. I think best time to travel is 0-12 months and maybe after 3 once the toddler stage is over
Get a really good and comfortable baby carrier!!
When I traveled with my newborn we really didn’t need much more than the basics. Diapers, wipes, clothes, booger picker, thermometer, nail trimmer, how you plan on feeding him/her, travel stroller, I loved my portable bassinet, minimal amount of toys
Don’t worry or stress about anyone but yourselves. Babies are great travelers and sleep most of the flights at that age due to white noise. Pack spare clothes for you and baby in case of a 💩🤢 event midflight. Babywearing at that age is great for boarding and tbh fab for London with a newborn. Book the skycot if it’s available. Feed baby or give them a dummy for take off and landing. Just a bit of mild suction helps them ease any discomfort of air pressure. But don’t stress too much on that front, we’ve been flying every month since our girl was 8 weeks old and it’s never been an issue.