We need some custom fields on the invoice, like Ordered By and Delivery Note. We are presently evaluating Invoice Ocean up against QuickBooks Online. They have a number of custom fields that you name based on your own needs and the data entered become part of the database and reports. Is this something you are considering?
You can find a lot of invoice customization tips here http://help.invoiceocean.com/Invoice-Customization?page=1.