You can create your own module. More info in documentation. http://ez.no/ez_publish/documentation/development/extensions/module/module_tutorial_part_1
You will have to use ezmail class. lib\ezutils\classes\ezmail.php
Using information collectors as you mention is also good way. If you create all inputs then you can edit/format only one tpl to set your own design from html mail (override content/collectedinfomail/form.tpl)
Remember to set ContentType=text/html in [MailSettings] in site.ini.append.php