It's called "The V Seat", a bit expensive, but I've read nothing but rave reviews on it. Apparently it was on that show Shark Tank (never seen it but know what it is) and has been very successful.

I struggled with perineal pain, and my wife with similar pain, with a variety of seats after even just 20-30 minutes riding - my sit bones just never relieved enough pressure - so this seat would have been something I wanted even without the prostatectomy.