I ended up moving from using a smartphone, to using an older flip phone and a tablet.
If I need more advanced functionality, I use the tablet, but for basic calls I use the flip phone. I prefer this since I only have to worry about the batteries once a week.
With infrequent use tablet with a good battery can go a few days between charges (eg, I use mine for mainly taking notes and recording lectures)
wifi coverage is good and I have a VPN so those are fine, bu tif there is an emergency, I can tether the tablet to the flip phone using bluetooth and get about 1.5mbit/s.
Hopefully one day these companies will figure out a way to make these phones go a week on a single charge with normal use. or at least add a second board that is essentially a PCB used in a dumb/ feature phone, then offer a way to switch to them if all you need to do is make calls and do other very basic things.