Your idea is interesting, annetta1.
However, adding the customer order numbers to the invoice is not yet possible, Thus, it will not appear when you create statements.
For now, the only customisation that we can do to the statement is to show the transactions a single line item or display each line item per invoice. You can use this link for reference: Create and send customer statements in QuickBooks Online.
We'll take note of your feedback because it will help QuickBooks Online Improve to suit your business needs. You can also visit this link to be updated with the changes: The QuickBooks Blog.
Let us know if you need anything else. We'll be right here to further assist you.