I would update the email template where it is set up more easily like actual emails (like outlook/gmail etc) where you are able to bold text, hyperlink, etc which would make creating templates a lot easier. Secondly, having a list to the side of the template creation with all codes would also make it easier for us to insert the certain codes needed to ensure that the emails are personalised ( {customer_name}, {tour_title} etc).
Update:
PaxFlow Platform includes a e-mail template builder that fully supports HTML e-mails. Install the PaxFlow - Automated Messages App on the Bokun Appstore or reach out to our team to try the feature with other booking systems.