Checkbox or Radio, specific use case

I have a very specific use case and it has led me to question the checkbox vs radio button convention...

Radio buttons are used when there is a list of two or more options that are mutually exclusive and the user must select exactly one choice. In other words, clicking a non-selected radio button will deselect whatever other button was previously selected in the list.

Checkboxes are used when there are lists of options and the user may select any number of choices, including zero, one, or several. In other words, each checkbox is independent of all other checkboxes in the list, so checking one box doesn't uncheck the others.

I have a scenario where the user has the option to attach a CV/Resume to a message from a list of CV/resumes that the user has previously uploaded.

The user doesn't have to select any, but only one CV/Resume can be sent with each message.

Therefore radio buttons aren't applicable here because the user can not de-select a radio button. Checkboxes aren't applicable either really as only multiple can be selected.

So what would be the control?

I've gone with checkboxes and extended the functionality to only select 1 at a time.

So I guess my question is, have I made the wrong decision extending checkboxes? And if so, what would be a better solution?

Thanks! Mitch