Soft-spot pain is probably from you weight-bearing on the soft-spot instead of on the ischial tuberosities of the pelvis.
Padding would just mash into the soft-spot and probably feel worse.
It might be useful to measure your center-to-center of your sit bones (this is what the butt-o-meter at the LBS measures) AND your outside-to-outside of the bones AND do a "cut out" test.
If your bone center-to-center matches the span of the center-to-center of the saddle cheeks, AND your outside-to-outside is 10 or 20 mm LESS than 137mm, AND you don't need a cut-out... then I'd start looking at top contours (less domed, more flat) before I'd even start to consider more padding.
(I'd suspect your Fizik is too narrow, and if the measurements seem to bear that out, I'd just get a wider version of the same saddle you already like)
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