Ive been using custom roms to greatly extend the lifespan of my phone (still using a xiaomi mi9t from 2019, running smoothly on A15, with lineageOS). Some apps, like banking apps, or gov apps sometimes require a stock android and locked bootloader. But, besides the stock spyware, stock roms become unusable in 2 to 3 years, forcing an upgrade.

Im thinking of getting a cheap 2nd phone to keep with stock android to use banking/gov apps and to leave at home. This way i could use my primary phone with a custom rom and have it working for way longer than 3 years, with less spyware, and wasting less money (depending on the price of that 2nd phone).

Does this seem like a decent strategy considering how android is moving?

Important question: If the cheap phone gets outdated, would it be safe to use it for banking considering i wouldnt install other apps or use a browser in that phone?

The brands available here (brazil) are mostly motorola, samsung, lg, xiaomi and realme (no pixels, nothings, fairphone, pinephones,…). What would be the best options for these two phones? The 2ndary phone should be cheap and reliable (gonna be used like once a week, but should last as long as possible) and 1ary phone should have unlockable bootloader and have good rom support for many years (i hope this niche wont die soon).

Banking on the browser is not an option anymore in my situation. I think it wont be around for long in the rest of the world too.