Hi Sophie,
You can use your objects associations to create tokens from other tables. When creating a token, set your token type to association and you will be able to see all of the associations you have access too.
If your domain model does not allow you to access everything you need, what I usually do is create a non-persistent entity with associations to all of the tables that I want to use in my email template and then use that as the object in my email template.
Hope this helps!