In addition to KrisFlyer miles, Flexicombo fares add free check - in baggage up to 20 kg, free seat selection on specific rows, and a flight change waiver. (upgradedpoints.com)
Something we managed when flying to London: Qantas would do free seat selection for their frequent flyers and it was $ 50 for me to sign up. (flightstofancy.com)
Those flying with lap infants (and their travelling party) receive free seat selection, which includes carrycots and / or child seats where available. (havebabywilltravel.com)