Companies that make allowances for disability:
Qantas offer a concession for disabled passengers and for a carer, in business class and in economy. But you’ll need to get a PWDA/Qantas Card (which they charge an admin fee for) and it’s subject to availability (ie not always available) so be sure to book your flights in good time!
Virgin Australia also offer a discounted fare for a carer to travel with anyone with special needs. Details here.