Dang, it's nice to find another 'Kashmir' Shaiva here, of all places!
Do you practice? (I mean this in the sense of practicing the inner yogas/meditation, not in the sense of joining a religion.)
(I found this post when searching for the word 'dharma' on LW, to see what the word means for the community. I actually think this post is def instructive, but still written from within a reductive lens that privileges the Astika schools rather than now.)
The book 'The New Diary' by Tristine Rainer has a variety of tools and methods for precisely this expansion of journaling (which go much beyond prompts, so if you're looking narrowly for just prompts then it may be the wrong level of abstraction), and claims that these tools and methods in fact constitute a basis set for the activity.
(FWIW, the book was updated multiple years after its publication, and the author claims that she hasn't found anything not covered by the intervening years not covered by the basis.)
Sir Gowers actually has a number of playlists around thinking about problems in real time; haven't looked at them myself, but may be worthwhile to mention that this series is one instance of multiple playlists of the same type, each focused on its own domain.