Hmmm, this might be a struggle.
However, I think what you're actually after isn't softer as such, but more compliant. Certainly the KWv3 will be that, albeit at a cost, but I've found the BC stuff to be more compliant than OEM too across brands. The 645, for example, now runs the BC BR setup, and whilst it's not as squidgy* as OEM, it actually rides bumps and lumps in the road better. I can still feel them, but they don't unsettle the car. Given the cost differential between BC and KW, I'd be tempted to try the BC first.
*Technical term.