I have read about jumping a lot because it's the easiest available method for me and I still couldn't do it. 10 stories is the minimum recommended. As long as there are no obstacles in the way chances are very high but there is always a chance of surviving.
Hitting head is the more certain way but if you can't try to land with the front of your body on the ground. The people who survive the most either get caught in something on the way like a tree or land on legs, knees slight bended.Try to not fall on your legs and keep your legs stretched flat if you can.
Do it at night if you can, less chance of being saved.
I know is hard but is better to avoid drinking alcohol, it increases your chace of survival because it relaxes the body.
Best luck if you decide to do, it's a scary way to CTB. Sending you love and I hope you find peace.