You answered your own question. You could probably just have one pool with 2 mirrored vdevs and achieve the same or even better, if you don’t need mirror performance a 4 wide RAIDZ2, this will yield the same space efficiency.
Bottom line is: you only have 1 copy. Period.
At least get another machine up, even better place it remotely.
Add cloud backups to your routine.
Have a look here:
Edit: for me it’s:
Most important stuff with backblaze (cloud)
2 local machines, one of which will move completely off-site soon. Just haven’t had the time to further look into my thread where I ask.on advice on that.
And a USB harddrive that’s currently NTFS but I will look into formatting it to zfs and store the occasional offline copy there.