Unfortunately SSDs have gone up in price quite a bit, but I would suggest a simple raidZ1 zfs mirror with enterprise SSDs, no need for additional boot drives.
(Sorry for the confusion, i wanted to write mirror not RaidZ1, must have been more...
I think it should still work, maybe you need to use the Debian archive repository.
But I think it will be easier to make backups of your virtual machines and containers, do a fresh proxmox install and restore your backups.
If you use a...