Should I rent a car?

So I’m doing a solo trip through NZ in March and in the past when I’ve taken a trip I’ve only ever done public transport whether it was a bus, train, or whatever. I like doing public transportation because it’s cheap and I get where I need to go without getting lost in the middle of nowhere. I’ve been doing a lot of research and it seems like NZ doesn’t really have great public transportation especially for the rural or off grid areas and seems like it would be really difficult to see all the good stuff on the South Island if I don’t drive. I would love some input or suggestions on the best way to get around during my trip. I’m a great driver and not totally opposed to driving however I drive on the opposite side of the road where I’m coming from so that does make me nervous. Could I drive for the portion of my trip on the South Island and get away with public transportation on the North Island? Or would it be best to rent a car for both. I would like to make the most of my time as well so if driving myself will significantly cut down on travel time then I’d rather do that. For reference I’ll be in NZ for 3 weeks. Thank you!!