Our next door neighbour has a beautiful vegetable garden.
She was showing me and Emma her tomato plant last week and it had these huge thick tomatoes growing off it. They were basically the same size as what you see at the supermarket.
She said that she just used seeds from a fully grown tomato that she already had.
It seems like it's a bit of a process to do this but it might be worth trying this November instead of just using the small tomato plant from Bunnings.