Hi Leah
I travelled back from aus when my boy was 12 days old. He slept pretty much the whole way. I then travelled again when he was 5 mths to canada and just recently to aus now he is 7.5 months.
6 weeks will be quite easy to travel with considering they sleep so much in the day / night already and pretty much feed consistently every few hours.
Some tips:
1. Get to the airport early and ask for the bassinet! Ring and request it if you can.
2. I took some muslin wraps or shaw and put them over the baby basket with some hair clips, this saved light going into his bed. I also took my breast feeding pillow so when they ask you to take them out of the bassinet during turbulance i put him on that.
3. Take a change of clothes for yourself! If breastfeeding wear easy tops to breasfeed in. The chairs are not the most comfortable for feeding, so the pillow came in handy.
4. Feed on take off and landing, this is good for their ears.
5. Blankets; it can get quite cool on the plane so wrap the baby up or put in a grow bag to keep warm.
6. A baby carrier is much easier to use than the stroller going through immigration.
hope that helps