How to make customized sales invoice default for customer group or specific customers

I am going to try to ask this in a way that both asks my current critical question and also hopefully helps me understand the logic (which so often escapes me) of the design of ERPNext.

From my extensive searches through topics here, I feel that my assessment of the prevalence of consignment based sales in the target market of ERPNext makes it slightly odd that it’s not obvious, however I am completely ready to take responsibility for my own ignorance and learn.

So, the idea is that we deliver multiple times to one customer over the course of a month, with repeating products during that time.
There isn’t an obvious or explicit consignment workflow, however this is what I have come up with:

  1. Make sales order .
  2. Make delivery and delivery note (with signature field on delivery note). (This relates to my other post about the desire for a POS-like simplified delivery app which would really help when as a small company I am dealing with delivery people who get overwhelmed with the complexity , touchiness and lack of offline resilience of the mobile user interface).
  3. At the beginning of the following month, an invoice is generated from all of those delivery notes minus any stock they still had remaining and customer is billed for that previous month.

What makes sense, is that when I make a sales invoice from a number of different delivery notes, it would either:
A. Put all same stock (identical products, or at least identical batches) together added to total, list totals of each product type, and then give grand total…
B. List each delivery note sequentially and reference the delivery note to the product delivered and signed for WITH that delivery note.
But what it does is just list all the product without any reference to which delivery note they were delivered with…
So it makes for a very confusing repeating list of products. *(this also makes it VERY easy to duplicate/omit and make mistakes)

The workaround I attempted so far was to customize the sales invoice item…so that the “delivery note” field was not hidden. But this was locked in the sales invoice customization.
So I further workaround I attempted was to duplicate the sales invoice and customize it as “consignment sales invoice”. In that duplicated doctype I could “unhide” the “delivery note” field.
But after trying every way that I could think of, I cannot figure out how to assign/ make default that “consignment sales invoice” to the consignment customer group (or even to the individual customer would be second best solution).
So I’m hoping for a solution for this, but I’m also hoping that someone can help me understand some “meta” to this that I might be missing…
It seems to me that this would all be fairly simple to build into “switch or choose” customization.
But I end up spending hours and sometimes (should I be embarrassed?) days attempting to solve what seems (from my experience with other systems) to be easy and common customizations.
I am considered to be fairly to rather intelligent in most areas, so I really would like to learn that “angle” to looking at this all from that would help it to be a bit more intuitive for me.
I’m not looking for the cookie cutter fix, it’s just that it seems like when I try to “make cookies” (figure of speach) with ERPNext I find myself trying to design ovens and mill flour and build a bakery when all I really want to do is make some cookies.
I hope my humor comes across louder than my whinging, I fully appreciate any help and will try to get smarter/better/more helpful and less helpless :slight_smile: