I would hold off on a dog right now. If you can't afford a larger place then you likely can't afford vet bills, nutrition for a large dog, and paid training. All of which are things you will need as a new owner who has never owned a large dog. It even starts with the puppy series of vaccinations they will need not just emergencies. Also, what happens if you get injured and can no longer run with the dog? This is a reason why large dogs need large fenced areas to run because our habits can change over time and they still need exercise. I also don't recommend getting a dog at this age because there are so many changing factors that can cause you to move or change your work or study situation where you can no longer provide for a dog. If you are mainly looking for self protection I would recommend carrying self protection like mace and doing self defence training classes rather than taking on the huge responsibility of a dog.