I remember Xubuntu and Kubuntu, I may look up what's their current state now. As long as you don't do anything stupid, you shouldn't get hacked, so maybe a hardened OS is overkill, but I will look into Whonix, but like I said, as long as it just installs fine and can do full disk encryption and run the Bitcoin related stuff and not have bloatware etc, and maintain it secure with updates, that should be enough.
Xubuntu and Kubuntu are fine, but they do not get LTS releases. Instead, they only get updates for 9 months like the other non-LTS versions.
You need to recheck these pages,
https://xubuntu.org/download/ and
https://kubuntu.org/getkubuntu/. Both offer still offer LTS version. But unlike Ubuntu which has 5 years support (10 years if you subscribe to Ubuntu Pro), those distro only receive 3 years support.
Makes you wonder why don't the device drivers just make it easier to make open-source versions of their drivers. Like what is there even to hide inside a driver that will give someone else a competitive advantage? That's all hardware.
At least for basic printing, CUPS[1] does the jobs wgere you don't have to use closed-source driver/firmware.
[1]
https://wiki.debian.org/CUPSDriverlessPrinting