Re: I've bought my last one
Hi. The other option if you are worried about security updates and other OS updates is to get yourself an Android phone that you can root. There are some great older but still newish phones that you get pre-loved at a low price. examples include the HTC 10, Nexus 5X, Xioami MI5 all for less then $150 USD.
These are easy to root and you can load the latest Android version 9 PIE and get monthly over the air updates from free ROMS such as Lineage OS ROM, AICP ROM and many others. just google a few and it's not as difficult as it seems to root and load your own ROM.
The benefits are you are not tied into a manufacturer and you get all the latest features and security updates without the "bloatware" (apps you don't need that take up memory, slow your phone down and consume battery).
Don't be afraid and have fun. if in doubt get a real cheap second hand phone and have a go.