Just found out that DHS does accept certified copies of the naturalization cerfiticate for initial passport applications. All we have to do is call USCIS and schedule an appointment to get a certified copy once we take oath. Getting a certified copy is free... but if your (original) naturalization certificate is lost in the mail it'll take $500+ (AND you get to deal with USCIS and VisaJourney all over again!) for USCIS to issue a new naturalization certificate.
Although there's some ambiguity here:
(A) USCIS says original must be submitted for passport application: https://www.uscis.gov/tools/how-do-i-guides/us-citizens/how-do-i-obtain-an-authenticated-copy-of-a-certificate-of-naturalization
For example, when you apply for a U.S. passport, you must submit the original Certificate of Naturalization, and you should also submit a normal photocopy that has not been authenticated.
(B) BUT DHS says certified copy is fine: https://travel.state.gov/content/travel/en/passports/need-passport/apply-in-person.html#:~:text=ALL%20%2F%20ALL%20%2F-,Get%20evidence%20of%20U.S.%20citizenship%20(and%20a%20photocopy),of%20the%20official%20issuing%20authority.
Your evidence must be an original or certified, physical copy. A certified copy is any document that has the seal or stamp of the official issuing authority.