I think all the Krav Maga suggestions are coming from people having watched a few youtube videos and being impressed. It isn't what you are looking for, functional Krav Maga for self defense would come after quite a long time.
It's also, in IMO, just a bit too much, the fighting skills I learned in the military and working for pmc's don't translate well to everyday life, they go too far as when you need that skill set your life is likely on the line. Breaking a wrist, elbow, dislocating a shoulder, smashing a nose and then stamping on someone's nose or face is far too far. You never want to be the person that does this to another human.
My recommendations for self defense go in this order.
1) Fitness and avoidance. Firstly, sprints and endurance, be able to run as far and as fast as you possibly can. This is the best self defense on the planet. Trust me, you do not want to be fighting people, ever. Secondly avoidance, just don't go places where you think or know you're likely to end up on a fight.
2) jiu jutsu and Muay Thai are both excellent to learn, Muay Thai has use in the push shove face off stage of an altercation when people are shouting and waving their arms like fat peacocks. Only a few months worth of Muay Thai will give you the ability to catch someone on the chin or button and end a fight before it has started, just be careful about popping people first. Jiu jutsu has more value overall as 95% of fights end up on the ground rolling around. And simply even a rudimentary level of jiu jutsu will let you handle and control another human.
I'm also of the opinion that most jiu jutsu places offer a more mature and safer environment to learn to fight. The first dozen times you train and then spa your adrenaline reaction will be quite surprising. Learning to live with that adrenaline I a jiu jutsu environment is ideal IMO.
I'll finish with my first suggestion, fitness, being able to run fast and hard for as long as possible. Shame of running away is a young mans fear you will have to put aside, you aren't in school anymore where you have to face people talking shit about you for the rest of the year, calling you chicken. Fighting is shit, and if you win or lose you will come away feeling terrible.