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You don't need to go out and buy hardware keys today. You should be able to use any FIDO2 key these days for SSH, as long as your server runs a recent enough OpenSSH server, which supports ecdsa-sk or ed25519-sk public keys.

Reputable vendors of those hardware keys included Yubikey and Token2, among others. You are really just using them as FIDO2 tokens, so go for what's reputable there.

If you are just getting started, you can generate and use software-backed keys (using ssh-keygen) and copy the public keys to servers' authorized_keys file using ssh-copy-id (or manually adding it). You should probably start learning this way (with plenty of online guides, and fewer risks of an old server implementation not supporting FIDO2 credentials), and then move to hardware keys once you understand the mechanics of copying around public keys, etc. Your password manager might also support acting as an SSH agent for key based logins - I believe Bitwarden and some others now do this, for example.

If you have an iPhone, the ssh client app Terminus can use the Secure Enclave of the iPhone to store your private key, which prevents all apps on the phone, even Terminus itself, from being able to read the private key. The private key is stored in hardware. You use FaceID to approve the login operation that ssh is performing.

I switched over to using that in Terminus recently instead of having Terminus generate and manage the private ssh keys.

Likewise, many Mac and MacBook machines have Secure Enclave too that can store private keys in hardware and works with the ssh client that comes with macOS. But I have not personally started using that yet. Will soon though. You then use TouchID to approve each login operation that ssh is performing.

Yubikey is cool too. I’ve used it mainly for other things than ssh.

Whatever solution you go with, have a backup or another way to restore access when your hardware key eventually breaks and cannot be used.

For example, instead of buying one Yubikey buy three and give each of them access to the same places. Keep one on you, one at home, and one somewhere else. Rotate between using each of them every couple of weeks so you are sure they all still work and that all of them have the accesses to all the same places.

In the case of ssh, you probably either have physical access to the target machine or you have VNC management from the hosting provider, etc, that you can fall back to if you misplace or damage your hardware key. So if you only use the hardware key for ssh and you have other means like those to get back in then having just a single hardware key is mostly fine.

A Yubikey, though simply generating ssh keys instead of using passwords would stop this MITM attack. So would changing the rounds and port of ssh on your system and the remote box making yourself an invisible protocol nothing would recognize.

Yubikey benefits is it stores the keys in the hardware if your laptop is compromised somehow or stolen they at least don't get all the ssh keys too

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