[Koha] Capturing a "consent" field for new patrons

Gentle Reader, We need to capture an email "consent" field when we add new patrons to Koha. Currently my solution is to have staff type "yes" or "no" into the borrowernotes field but what I would really like is to have "yes" and "no" radio buttons, or failing that a drop-down with "yes" and "no" as the only options. And it would be really good if the field was labelled "email consent" on the patron entry form. Any suggestions gratefully received! Best Regards, Chris Brown