So, I want to do some martial arts, for self defense. Ideally one that will be useful without giving me CTE, or any long term bad stuff, even though I feel this is already asking for too much 
I don't live in the U๐๐ so gun related stuff isn't really an option.
I'm somewhat heavy, with a year of experience in lifting, and my cardio is not the best, but I can do long walks (of 1 or 2 hours) before getting tired.
I'm going to move to a bigger city in September, and there's a lot of stuff available, so you can comment on the more niche options.
So yeah, any advice from your experiences is welcome lol
If I had known people started arguing over my post I wouldn't have made it.
I second that Judo and especially Jiu-Jitsu are probably what you want to do to minimize risk of long term injury and get useful training. It depends on where you're training, but in my experience you're less likely to get acute injury from Jiu-Jitsu (less likely to take a bad fall) and it has more groundwork, which is important for self-defense. Judo is still helpful though.
Most striking martial arts either give you a higher risk of acute injury than you're probably okay with, or are garbage for any purpose other than general fitness. That said, general fitness is still a good thing and you are much more likely to get through a self defense situation unless you have good cardio, so you should seek to improve it even if you can only pursue it via stationary bike at a gym or something.