Mario...
Here is THE best way that I have found to DeEss a vocal. Since you have Studio One Pro, you will be able to relate to all these instructions...
Expand the vocal in an area where you know there is an Ess (that's what I'll call them - they can be other things - "cht" etc.) Solo the track to listen - easy to hear them that way...
There is always an identifiable wave shape there. It is kind of cigar shaped and it will be very dense (picture 1 - right in the middle).
Cut on either side of that.
Right-click that cut section and select "Decrease Volume".
For a few you might need to do that twice, but generally, once is enough.
This almost ALWAYS works for me. And the result is almost ALWAYS better than using any plugin I've ever tried.
Pictures 2, 3 and 4 show examples that have this done...
Pic2 is an Ess at the beginning of a word.
Pic3 is an Ess at the end of a word.
Pic 4 shows the phrase "the sun". The first blob ("the") is left alone. The 2nd blob is the actual Ess. The third blob is "sun" which was a bit harsh. This part of the vocal now sound just as it should...