I understand very well what you can feel. You don't know how your body will react and this is frightening if you think about that previous bad trip. A huge difference between DMT and LSD is that DMT alone last few minutes. So you can test growing amount slowly with enough time between tests to check how you react.
Just start to smoke a bit. No need to weight anything. You just inhale a puff.. see what happens and what you feel.
Few min later you can see that everything is ok. Then smoke a bit more... Wuuuuuuf a heavier body rush should happen.
OK that's scaring but it lasts anyway few minutes. You can continue later or the next day.
That way you reassure your body that it can 'handle' the spice.
You will probably feel that your heart accelerate, but that's not the DMT, just the anxiety due to the rush.
When you feel ready, decide for the appropriate time (a quiet evening for example), take eventually a benzo one hour before and go for a bigger dose
If you took the progressive way described above, you may have reduce your fear to 50% (you trust your body).
25 % may be taken by the benzo, the last 25% is your work (I did what I did, no regret, let's see what happens)
No doubt that new doors will open