you should list more information about your amp?The only item you mentioned is rail-to-rail output swing.You have to provide a power signal to load?? Maybe power amplifer output stage is not suitable for your application.which load you have to drive,res or cap or other.
the load of my operational amplifier is the gate of another MOSFET which is a input of another differential amplifier
the goal of this (feedback) operational amplifier is to convert the input current signal to output voltage signal(transimpedance amplifier), and it is required that the output voltage signal can swing from Vdd to Vss,therefore I want to design a buffer which has large output voltage swing