3 hours is definitely enough for Narita.
Minimum connection domestic to international is less than 2 hours, and the ITM-NRT flight is usually on time.
You can even check your bags through to the OZ flight. Just go to the "international counter" at Itami(Osaka) for them to tag your luggage through.
Osaka (Itami) : South Terminal Counter No. 11
https://www.ana.co.jp/en/jp/domestic...n/transit.html