Who warned you that your battery would get burned out if you didn't use the USB C cable? Thats not true.
You can use all the old lightning cables & chargers from your previous iPhones/iPads without harming the battery.
Ideally they would be the original cable/chargers provided (Apple branded), or a reputable brand (such as Anker) rather than just some cheapo crap from a gas station.
I don't see why using an adapter would be a problem either. Again, from a reputable brand.
I've plugged my iPhones into my vehicle for CarPlay over the last 3 years using a USB A to lightning cable from Anker.
My batteries have always still been 100% health when I turn them in after a year of use.
IMO, the main thing you should avoid doing is letting your charge fall below ~20% or so. Charge your phone over night all night and top off as necessary during the day.