Your seat is TOO soft??? Might want to have that checked; never heard anyone say that about it before.

Seriously, though, there is a post elsewhere in this forum describing how one member in the UK had his seat recalled early on. I forget exactly why, but I think some of them may have escaped from their maker in Italy without enough padding in them, which could cause exactly what you report. Best check with your dealer on that issue.
Likewise, I would double check tyre pressure before tinkering with suspension. It makes more difference than you might think. I found that out the hard way. And BTW, although preload adjustment is possible, Triumph do not consider it a
user adjustment on either the Street or Daytona. Be safe!