If you're consistently worried about getting attacked with a knife, I see a couple of options for you. One, you could change your lifestyle so you weren't constantly getting attacked with knives, which would be my choice. Two, you could just get clothing that would protect you better when you were attacked with knives.
If you're a number two type of person, might I recommend these knife-proof shirts from Nihon Uni of Japan. Coming in both short and long-sleeved varieties, they'll set you back anywhere from $190 to $590. They can protect against slash attacks, but be warned, if you get a straight-up stabbing it won't do much good. It uses an ultrahigh molecular weight polyethylene fiber to do its protecting, but without stab protection I'm not sure it's worth the costs. But hey, you know what kind of knife attacks you're receiving better than I.