Home protection/self defense items for a woman living alone?

So this is not my first time living alone and I haven’t had issues feeling unsafe in my home in the past, however several months ago I moved to a place kind of in a shady part of town and my downstairs neighbor, who hates my guts, is mentally ill and has anger/drug issues and has been harassing me lately. All in all, It’s made me kind of frightened to be home. I’m looking for some protection items I can keep in my home just in case. As of right now, I have a door stopper and I make sure to check my windows and doors every night before I go to sleep, but I’d love to have some sort of self defense. Anything you can recommend would be much appreciated!