Istikhara whilst in a Haraam relationship

I am a muslim girl who has been in a relationship for some time now and we wish to get married to save ourselves from sin and that we really want to spend our life together in a halaal way, I wanted to know considering that we already know each other and that there has been physical contact between us how would we go about reading istikarah namaaz and what signs should we look for indicating whether this is the right deciesion?Because we already know each other and we realise by having the physical contact we are sinning therefore we are trying to correct this but it also could cloud our istikarah judgement, so considering this how should we proceed from here? Because we both wish to proceed in the rightful manner. If possible I would like to know if there are signs that would be without a doubt and clear because we wish to recieve Allahs guidance before we proceed.