Well, if it comes to Flash updates, you might prefer Chrome which seamlessly upgrades itself and the used Flash package in the background. On the downside, slight UI changes might happen with new Chrome versions.
Also Linux is still an option. It could be configured for all the needs (contrast, font size, clean UI, autologin, ...) and has some additional administrative features like automatically upgrades in the background (including Flash, if Ubuntu is still providing that meta package) and every configuration could is also openly reflected in the file system which might help doing remote support and backups. Also it might prevent the usual Windows/Mac malware downloads.
Also Linux is still an option. It could be configured for all the needs (contrast, font size, clean UI, autologin, ...) and has some additional administrative features like automatically upgrades in the background (including Flash, if Ubuntu is still providing that meta package) and every configuration could is also openly reflected in the file system which might help doing remote support and backups. Also it might prevent the usual Windows/Mac malware downloads.