A tripod is def a must have.
If you want to get POV footage, you could use any kind of gimbal that counterbalances your movement of the iphone, for example from dji the osmo.
For hands free operation, you could get a gopro (8 and upwards, as they have good enough stabilization afaik) and a chestmount. With their linear mode you can also get rid of the fisheye-lens look.
Have fun, and looking forward to the results on the missus.