I am as dense as decent block of lead, and have a poor short term memory.
I match fretboard position to the key. I then write the position on the sheet
using roman numerals for the position,
I Gb (6b) Db (5b)
II G (#) D (2#)
III Ab (4b) Eb (3b)
IV A (3#) E (4#)
V Bb (2b) F (b)
VI B (5#) F# (six #)
VII C G
Most of the time C is played in 2nd position.
This info was 4 finger lifted (bass joke) from Alfred's Teach yourself to read music for guitar, which by the way, emphasizes single note playing, and not chords. (sounds like playing bass) Since I sometimes practice on a guitar lower 4 strings (sounds like a piccolo bass doesn't it), I am also forcing myself to read treble.
Yes, there is occasional shifting, but in trying to minimize left hand movement, I can use the technique on my fretless.
The above does not work well on an upright.
Second trick is to play the B part of the music if the music is available in SATB format (choral)