For the love of god, don't eyeball. An objective measurement could mean the difference between success or pushing yourself into further pain if you fail.
As far as I can tell from searching it up, the two most common groups of fatal falls are 0-20 feet and 21-29 feet falls.
The most common fatal injury from falling is either getting impaled or from skull or spinal fracture. I suggest going head-first into the concrete so that you will at least be brain-dead. When your brain-dead, you are essentially mentally dead without really being biologically dead, so this could be preferable.
Just try to get something higher. I can't condone doing anything like trespassing, but if you can pretend to be in need in assistance to a neighbour on the highest floor, then ask for a tea, and jump head first out off the balcony while they are distracted, that could be a good option. It's not necessarily trespassing or illegal since the owner let you in on a valid pretense and was not coerced, but wanted to give you tea out of the goodness of their heart.
My philosophy has always been that unless you are sure that you really want to CTB, then don't. If you've tried everything, then you may want to consider it. If you still want to live your life or haven't tried psychs, SSRI's, experimental treatments in clinical trials, then do those first before really thinking about it.