I used to do self-harm... I burned not cut, and to me it was like I was transferring the pain to my body and out of my soul. For that moment, the pain was something tangible that I could touch and understand. I don't know if that is what it is like for others who self-harm.
What you are doing needs to be attended to even if it is somewhat harmless.
Are you taking action to deal with the suicidal feelings? (Therapist, meds, etc).
I was 15 when I made my first attempt. I survived by luck (a friend took me to the hospital). I wasn't treated for depression until I was 25. That was a long long time to suffer and I hope you don't have to go through that.
My heart goes out to you.
Is smothering yourself symbolic of how you're feeling? Feeling smothered?
That is not a very constructive coping mechanism. I would suggest talking to a doctor and ask to speak to a counsellor or psychotherapist.