What's the least disruptive way to change my Apple ID?

Assuming you use a 3rd party email address, just change the email address you use as your Apple ID. It's fairly simple and straight forward.

This will not disrupt anything, and maintain access to all your purchases and content.

follow the steps here ➜ Change the email address you use as your Apple ID - Apple Support

Maybe using an alias would help: Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support - "An email alias is an email address that conceals your actual email address from a recipient. An alias can help you manage the email you receive, and monitor the sources of unwanted messages. You can both send and receive email from an email alias using Mail on iCloud.com.

Kenabler wrote:

Thanks, Phil0124. I am using Airmail

AirMail is an app, what I meant was if the email address you use as your Apple ID is from a third party provider such as Gmail, Hotmail, or your office or school, it can be easily changed on your Apple ID without affecting your Apple account's purchases and content.

You would have to add the new email account, whatever it is, to the Apple Mail App or the Airmail app.

If you use iCloud as your email address, i.e your email address is yourname@icloud.com, then you cannot change it.