Is my action of disregarding the whispers (waswas) during prayer correct, and when do I base (my decision) on the lesser (number of rak'ahs), and what is the ruling on the aforementioned prayers that were interspersed with doubts?

The obsessive thoughts have greatly affected you, and you must struggle against them and not succumb to them or give them any attention. Your prayers are valid and you are not required to repeat them, nor is the prostration of forgetfulness (sujud al-sahw) necessary when in doubt, as long as you are suffering from obsessive thoughts. This is because the jurists have stipulated that a person afflicted by obsessive thoughts should not pay attention to them and is not required to perform the prostration of forgetfulness. This is what is incumbent upon him until Allah grants him healing. Getting rid of these doubts and obsessive thoughts is achieved by seeking refuge in Allah Almighty, completely disregarding them, and not paying attention or responding to them.