I say the durood ibrahim after the regular morning and evening doas. Specillay after the saidul istighfar. Beacasue as I know its necessary to send salawat upon our prophet ( sw) in our duas. So, it is ok to do this after the morning and evening duas?
There a number of wrong things you are doing!
There is no such thing as sujood istighfar. This is a clear innovation and it is prohibited.
It’s also not part of the sunnah to offer salutation upon the prophet salla allahu alaihi wa sallam during the morning and evening athkar.
You can offer such salutation throughout the day and night as many times as you wish.