Try DR Roundcore 12s. That's what I currently have on my jazzbox. Roundcore strings (as opposed to the common hex core) sound better IMHO and definitely have less tension than the hex core equivalent.
13s are the next step up from 12s, but that's if your dead set on not using any vibrato in your sound.
-The 7 and ERG Chord Melody [Jazz] Thread-
"If Stravinsky's music is that of the Earth, then Meshuggah's music is that of the Machine"
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