"We could have had what we wanted, if we 'had' decided with ...."
Don't forget the auxiliary verb (had) when constructing the past perfect simple tense.
For the end of the sentence, I'm not sure exactly what you're trying to say when you use the word "intention". If you are trying to say that - had you been more sure of your decision you would have got what you wanted, then you could use the word "conviction".
"We could have had what we wanted, if we had decided with conviction."