Customizing "Notification Email" templates (Invoices)

Customizing "Notification Email" templates (Invoices)

Hi
I'm relatively new to Zoho and have been trying to customize the Email Notification Template for invoicing, and I am current using the free plan as I have a small home business.

I'm struck by how poorly these email templates look and the very limited options Zoho gives to customize them into something that looks at least reasonably  professional. There are many great features in this app that I already really like BUT this one issue seems like a real "flat spot"! 

Is there a way (3rd party app perhaps??) that users can create more appealing / user friendly email notifications please?

Many thanks in advance. 
Edward