OP, I am so sorry, you have been though a DREADFUL time.
Of course you are incredibly distressed to have been through all that and lost a breast, and have such lasting impact when / if it wasn't necessary.
Being glad and relived you have not got cancer is one thing, and I am pleased that you do not have cancer.
But that doesn't make it all right to have suffered all that if it wasn't necessary.
Highly suspicious that the consultant is trying to steer you into a 'thank goodness, good news!' response.
A mistake was made in the treatment of one of my DC's some years ago (NOTHING like what happened to you, nowhere nears as bad, though had it been worse it could have been) . All members of the team involved in DC's care immediately co-operated with a full hospital enquiry, which was started voluntarily. The consultant self-referred it - although the mistake wasn't directly the consultant's work, but everything, from the consultant's instructions (including handwriting) to the lighting in the room where it happened was looked into. We didn't even have to ask. And we were given full access to all findings.
I don't know what happens in non-NHS settings.
Take your time, OP, look after yourself, know that you are not wrong to feel anything that you feel.
Does the hospital have a complaints policy / procedure?
Was it funded through an insurance scheme? Maybe they would know how best to start an investigation - apart from anything else, they have potentially paid for unnecessary procedures.
You need to know all the facts. What or if it could have been avoided.
I wish you strength and luck OP.