My experience with local seat places:
- I had Viking Motorcycle Seats in Kent rework the stock one for my old SV (2005). I didn't find it any better and it was so much taller I needed to fit risers.
- I inherited one from another company in Coventry
http://www.cmseats.co.uk/ for the 2016 SV. This was a cover and padding. It looked good but I noticed no difference and sold it on.
I'm sure it can work, but you need to know what you want. Do you actually want it firmer or softer. If you think you want it softer, it may be that's because it is actually too soft already and you are sitting on the pan. Also where do you sit, at the front, middle, or back of the seat. You may find that if they plan for this, you can't then move around as well.
From what I have read, the new SV seat is difficult to work with because of the shape of the pan. But you want one that doesn't tip you forward as much.
The stock shape and padding is awful. Such a seemingly minor thing when buying can ruin the whole bike.