You might want to let your cat roam freely outside but it can be dangerous with cars, dogs, and malicious humans lurking about. Rather than deprive your cat of the outdoors, you may want to put it on a harness so you can walk it safely outside.
To walk a cat safely, you need a harness so consider the best harness for your cat. Keep in mind that some cats might prefer to walk around on a leash while others might be perfectly happy being carried around in a stroller or backpack. So think of the best way to get your cat outside where it can be safe and stimulated at the same time.