Pool safety for 15 month old?

I want to take my 15 month old swimming with me in a big pool so that I can get in with her (instead of just her kiddie pool). What is the best thing to help keep her safe? I have heard about swimsuits/wetsuits with flotation devices in them, and toddler lifejackets, but those start at around 2 years old. I will be holding he the whole time, but would like to feel a little more secure with her being in the water with me. Any advice?