Indeed, these ways of doing things can help meet some of @ConorSheehan1 needs.
Nevertheless I would like to testify my need that there is also this “Comment” feature that ConorSheehan1 describes: A reply that is added under a message but does not add to the main thread.
I will study the proposal of @angus who proposes this plugin :
Do you know other people who express a similar need? Similar topics? Do you have any advice on how to search or work on the existence of this feature?