While this doesn't address the issue of 6/8 from a notational perspective, there are some new styles that came along with BIAB 2019 that have an excellent, slow 6/8 feel.
These have a tempo of 40 bpm (from a 4/4 point of view).
To isolate them, go into style picker, click on the "Tempo" heading to sort by tempo, scroll to the top, select one and have a listen.
I was quite excited when I found these
