Any weapon you use will require that you be trained in its use or it may be ineffective, or easily be taken off you are used against you. As you need training, your first best weapon would be your hands as they will always be available. Train in Karate or JuJutsu styles. There is no such thing as a non-lethal weapon. You can kill with a finger or by hitting the temple with the edge of a can of mace. For self defense that meets conditions 1 and 2 you might try carrying a short stick the size of a long pen (or a pen). Again, training in the expert use of it is recommended. Unless you master something you will not do well in a fight (except by accident). There is no free lunch, make the effort. If you are robbed, say held up with a gun, the weapon that you use is the action of handing over your wallet. That’s what may save your life, not using that ‘weapon’ may lose your life. Weapons can be deceptive. Talking can be a weapon, also running away. A weapon is a tool or method that achieves your aim against opposition. Your first aim is to live. A secondary aim may be to defeat an opponent. But to do that you need the intent, the weapon and the skill to use it. Your opponent may be better at using a weapon than you are, how much has he practiced compared to you? You would need to be able to draw out your weapon before he used his; you drawing, he just pulls the trigger or stabs with the blade, who wins? Has he a mate behind you or nearby? Take a Self-Defense course and you may see just how easily a weapon can be taken off you. There is also the use of strategy or deception, such as being disarming to disarm.