Sending html email and using static template

Hi guys

I'm sending html mail w/o any trouble, using email library
Now, I'm need to add some design to the "newsletter" system I'm building with CI

Which would be the best location to store images, css, etc. for the email template (relative?, absolute?) to be used within the email library, and how should I do to use and replace variables like {sender_name}, {sender_message} in the view (html template)

Thanks a lot in advance

Enrique
https://beza.com.ar