Custom fields on invoices/quotes by using metafields or alternative method

[Sten21]

First of all, we dont want to use any app.

We are trying to use draft orders to create quotes for our customers (since shopify doesnt have a quote creating functionality).
We however need to add several fields and information for the specific quote and for the customer.

Im trying to use metafields to edit the draft order code template with a rich text.
Im able to add information to the metafield when creating the draft order, but it is not visible when pressing "review invoice".

Does someone know how to add additional fields of custom information to the invoice (quote in this case) that will be sent to the customer (without having to edit the code for the template each time)?