Toddler swim device

Any swim instructors out there? What really is the best flotation device that actually allows a toddler to learn to swim and isn’t too bulky? I’ve read conflicting things about the Puddle Jumper (and how it keeps the child more upright and then they can get a false sense of security from them as well). What is something that helps them float and gives them a little boost, but allows them freedom to move their own body and actually practice swimming?