It took me some time to find out, how much to add and what I wanted in the end.
After comparing a lot of versions I knew less was more.
No dropped D because it shouldn't sound too much like lute. Also in the original cello score the deeper bass notes come in the middle of the piece. (edit: ok, I added a dropped D version too)
The added basses only underline some harmonies or build a room or an Orgelpunkt (pedal point) and don't build an additional melodic voice. (bars 22-28).
Not transposed to C because then it sounds too much like guitar or piano and the slurs at the beginning don't work (bars 1-6; 15-18).
Kanengiser's cello-transcriptions gave me the idea to look for linear melodic lines and broken chords. The notes of the broken chords should be able to sound together=be on different strings. (eg. bar 7; 10; 27-28)
The fingering should reflect the polyphonic structure and allow a fluent interpretation. It should feel a bit like playing cello. (I don't play cello)
The chromatic part in the end should allow to become louder and more have more volume so you get 2 instead of 1 note. (bars 37-38)
I got inspired a bit by this interpretation:
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