I’d recommend DMARC, sure - every little bit helps! But only because your SPF and DKIM are already aligned.

If you want me to check your work, shoot me a DM with your domain and I can take a look after you’ve done it with something like mxtoolbox.com (bookmark that one too, it’s good for checking your records after an edit to make sure the edit went live - just give it up to 72 hours). Or, a screenshot of the settings you’ve entered for the record, and I can validate for you (or mark it up to show changed if they’re needed).