In NSW self defence is only a defence against a murder charge if there is a threat to people not property or trespassOnly if the police can prove he entered your house. See my post above. This is actual advice given to me by a serving police officer.
Reasonable force or Legal Force can be defined in self defence terms (from the above site)
Self-defense is a defense to certain criminal charges as well as to some civil claims. Under both Criminal Law and Tort Law, self-defense is commonly asserted in cases of Homicide, Assault and Battery, and other crimes involving the attempted use of violence against an individual. Statutory and case law governing self-defense is generally the same in tort and criminal law.
A person claiming self-defense must prove at trial that the self-defense was justified. Generally a person may use reasonable force when it appears reasonably necessary to prevent an impending injury. A person using force in self-defense should use only so much force as is required to repel the attack. Nondeadly force can be used to repel either a nondeadly attack or a deadly attack. Deadly Force may be used to fend off an attacker who is using deadly force but may not be used to repel an attacker who is not using deadly force.
In some cases, before using force that is likely to cause death or serious bodily harm to the aggressor, a person who is under attack should attempt to retreat or escape, but only if an exit is reasonably possible. Courts have held, however, that a person is not required to flee from his own home, the fenced ground surrounding the home, his place of business, or his automobile.
The bolded bit is the most important. You cannot use a knife on an unarmed person. ( but if you have a spare non-set knife then place it in the intruders cold hand) . If there are other people in the house you will/should be able to be exempt from the requirement to flee/escape





