I won't try to talk you out of steel, but fwiw with carbon you don't feel every bump and crack in the road. Carbon offers a rather smooth ride, which is why they add carbon forks and seatposts to aluminum bikes.
As for sudden failures, that's not really a problem either. The damage is generally caused by an impact like a crash or hitting the frame against something.
Regardless, I don't think being on the short side necessarily means you need a WSD frame. A small version of a non-WSD frame might fit you fine, depending on the frame dimensions and your reach, inseam, etc.
- Gray 2010 carbon WSD road bike, Rivet Independence saddle
- Red hardtail 26" aluminum mountain bike, Bontrager Evoke WSD saddle
- Royal blue 2018 aluminum gravel bike, Rivet Pearl saddle
Gone but not forgotten:
- Silver 2003 aluminum road bike
- Two awesome worn out Juliana saddles