Hipshot Triple Lockdown individual string bridges with the GT piezo saddles installed. They will give you a 15 mm spacing. I have them on a Peavey Grind 4 that I de-fretted and added a 5th sting: High C.
I am running a pair of EMG 40TW-X pups thru an EMG BQC System. The graph tech acousti-phonic kit is next up on the additions. (budget)
E and C strings are about 1.5 mm in from the edge of the fingerboard but that works fine for me. Neck is 70 mm at the bridge end and 40 mm at the nut. I have a Graph Tech TUSQ 43 mm nut precut that extend a bit over the edges but gives me near perfect spacing and the 1.5 in from the edge.
Hipshot has Graph Tech piezo saddle equipped Triple Lockdowns in stock. And I highly recommend them. Although they do require drilling and careful inletting work. Still very much worth the effort.
The individual string definition on my bass is noteworthy. I was messing with it just after installing the individual bridges (with 4 strings
got anxious) and my son came out of his room and asked if I had a new bass. That noticeable a difference. The Peavey is a neck thru with string thru design. I have my strings anchored to the bridge. I have listened to several GT Ghost equipped axes and I am sold. FrankenBass lives.