For mail that you're sending yourself, from your own infrastructure (e.g. the envelope-from address matches the header-from address), DMARC + SPF should be sufficient and is easy to implement.
For third parties that are sending on your behalf, you'll likely need DKIM - but that will be implemented on their side, and all you'll have to do is add the DNS record they give you.
For third parties that are sending on your behalf, you'll likely need DKIM - but that will be implemented on their side, and all you'll have to do is add the DNS record they give you.