Unfortunately there is no post-save-action in DFFS because the default SP save functionality redirects you without letting you grab the new ID. You can do it like described here, but depending on how your form is set up it might not be an option.
I actually use DFFS “save and redirect” on newform for most of my projects now. See attached screenshots.
Newform config is minimal, requesting only basic information in order to create the item, all of the more complex form logic and configuration is on editform.
End users don’t really notice the continuation of the form after the redirect, and I don’t have to manage the separate form config on both newform and editform. Obviously once in editform you can use the item ID wherever you need to.
That seems like a good workaround. Ill give it a try. FYI: in my scenario I’m creating a range of list items in a different list referencing newly created item in the current list. Will probably put a spinning wheel on an Edit form while those are created.