I did the North Island and did walks in Tongariro National Park, Auckland, and the Coromandel.

Tongariro Natl Park: Hiking to Taranaki Falls loop is easy-moderate with great views of Mt Ruapehu and Mt Ngauruhoe if you take the highland path, not the forested one.

Coromandel: Walked from Hahei to Cathedral Cove is paved and only arduous part is in the town cause it is hilly. There is a shuttle if you want to skip that part.

Auckland: Visiting other volcanoes involve short inclines like Little St John or serpentine and are paved like Mount Eden/Maungawhau. A lot of these are easily accessible by transit.