As daft as it sounds you could have sidestepped a lot of these issues by buying a Lumia 950 XL from CEX for less than £80 https://uk.webuy.com/product-detail?id=snokl950xl32gbunlb&categoryName=phones-windows-phone&superCatName=phones&title=microsoft-lumia-950-xl-32gb-black-unlocked-b&referredFrom=boxsearch

Windows 10 Mobile is still a fully functional OS and whilst it lacks a lot of more modern apps, many of them can just be accessed via a web browser (like your bank) and it is such a minority in market share it is not even a target for criminals.

http://allaboutwindowsphone.com/features/item/24515_SevenreasonsforlovingandusingW.php

Onedrive backups still work or you can just do it the old fashioned way and download things to a desktop.

Best of all the camera can still keep up with modern handsets:

http://allaboutwindowsphone.com/features/item/24051_CameraheadtoheadLumia950XLvsAp.php