Further collection questions: "next"/"prev" for deeper sub-folders

So far I am moving good into Grav. Now one of the “books” I have has a deeper structure:

\default.md then I have 01.toc, 02.preface-tr… corresponding to different chapters in the book. Then, for 04.01, I should have 3 sections of that chapter: 01, 02, 03.

Now the issue is: the “next”/“prev” works only on one level: toc -> preface-tr -> preface -> 01 -> epilogue per se. I want to have 01 -> 01.01 -> 01.02 -> 01.03 -> 02.01 .... -> epilogue kind of navigation.

I know I may counter this by moving the structure 04.01\01 up one level and make it 04.01.01 but this may make my folders too many.

Any best practice?

Can anyone help on this?