I've done numerous trips with Qantas as well as Singapore, both of them who are excellent with children. Infact the last Qantas flight to Tokyo, my 9mth old daughter spent more time with the attendants than us. At 13 mths we flew with them to New York, and again they were really helpful.
Is your son going to be exactly 11mths at time of travel? I'm assuming you are talking about the CARES restraint system, but it specifies a minimum age of 12mths. Although it is a recommendation by the company, best check with the airline you choose to fly with. When we flew to Singapore, my daughter was just a week shy of her 1st birthday and the Singapore staff were more than happy for us to use it, as her weight was considerable for her age.
The only advice I can provide are things you'd probably already know, such as taking his favourite toy, favourite blanket, a bottle for feeding on take off and landing. Also be sure to take a padded nappy change mat as the change table in the toilets are extremely hard. Both airlines have reasonable selection of baby food but we found that at that age, you're better off requesting a special vegetarian meal and mashing it yourself.
If you have anymore questions feel free.