I have an attached 3rd party battery charger that also serves as a protective case. My iPhone battery would not last a day, and the Apple Store actually suggested something similar to below. I LOVE it. It is now about 18 months old. When new, I could go 5 days before the remote battery needed recharging. Now, it lasts about 3 days. (I’m a light phone user, however).
It is phone-specific, so you would need to check if something similar is also available for the 12 mini: https://www.amazon.com/dp/B0C6Q4MH7P?ref=ppx_yo2ov_dt_b_fed_asin_title
I would gladly keep my current phone, except many of the APPS I use or would like to use, will either no longer update or I cannot install (because the ios will no longer update).
The main downside is the added weight, but it was actually not that much different from the newer larger phones.