Flex IO v2 2.5Gb
This Flex IO v2 2.5Gb module is the sweet spot for these HP minis. It’s easy to swap in, it showed up immediately in Proxmox, and it uses an Intel controller (i225-V), which is exactly what I want if I’m doing pfSense or OPNsense stuff.
You'll be taken to Ebay to complete your purchase.