Warding an ECIES setup against MitM: ECDSA?
Yes, if you want to protect the message you could use sign-then-encrypt or sign-then-encrypt-then sign to provide authenticity and integrity. Without it an attacker may change the bits of the ciphertext, or simply create an encrypted message.

ECDSA would be the logical choice if you're already using ECIES. It may still be a good idea to use separate keys for signing and encrypting though (if just because you need the keys on different occasions).



You need to trust the public key of the other person before signing or encryption makes any sense though. It's OK not to trust a CA, but in that case you need a different way of performing key management within your PKI.

You could use separate channels to confirm key fingerprints, you could use a web-of-trust, share keys by sneakernet (memory sticks) whatever. But if eavesdropping is possible then 9 times out of 10 so are MitM, so you should make sure that an attacker cannot substitute the public key with their own public key.