Although we haven't had the opportunity to try any of them, based on the shapes and materials, I'd say that Pfun plug from Njoy, the Aneros vice, the Medium or small Pure Plug, or the Janus Anti-Shock from Zini could all be good options. Another option would be the Plug of Lust from Orion, although it isn't specially shaped for Prostate stimulation, I imagine it might work. Mine is the Large model and it stays in place well.