> When the iPhone 12 is released I’ll switch to USB C
Depending on what standards your existing ports support and what power input the iDevice can accept, you may find that a simple A->C adaptor will suffice. You may not get the fastest charge possible so in that case will want to move over sooner rather than later, but this may be an inexpensive (in terms of money and effort) stop-gap measure.
Why wait for the iPhone 12? The current iPhone already charges significantly faster over USB-C than USB-A, as do all iPads released in the past ~3 years.
There's really no reason to worry about it. Battery replacements (at least from Apple) are $70, and all modern phones have sophisticated battery management controllers.
Also, fast charging your battery more often could be better since you're not fully discharging and recharging your battery.
Depending on what standards your existing ports support and what power input the iDevice can accept, you may find that a simple A->C adaptor will suffice. You may not get the fastest charge possible so in that case will want to move over sooner rather than later, but this may be an inexpensive (in terms of money and effort) stop-gap measure.