My son has always loved the water and never had a fear of it. That was a huge safety issue for us since he also could not swim and sunk like a stone whenever he was in the water. Every time we took him to the pool, I was a nervous wreak when he was playing near it and when we were in the water with him, one of us had to be constantly holding him even in the shallow end because his head was just under the water line.
We decided we need to find something that he could wear when we were at the pool for safety reasons and something he could go in the pool with as well. In Target we found the Learn to Swim 1-2-3 floatation bathing suit by a company called Aqua Leisure. It looks alot like one of the old fashioned bathing suits men used to wear way back in the day. It has foam pads built into the front and the back of the suit similar to a turtles shell. The pads allow the child to go into the water and float while leaving their arms and legs free so they can move around unlike if they where holding on to a float or had a tube around them.
For the most part the suit worked well. When he was just playing near the pool I was not as nervous because I knew the suit would give us a few seconds to jump in after him if he fell in. In the pool, we still had to be there with him but did not have him hanging all over us. There are very clear instructions on the suit that it is not a life jacket and the child should not be left unattended. I experienced this first hand when my son flipped over on his belly. Because there are pads on the front and the back, when he flip on one side, it is hard for him to flip back over. There was a time or two where he went face down in the water and needed help to turn back up. My other word of advice is to make sure the suit fits tight. We bought ours a little big and when he got in the water, the pads caused the loose part of the suit to rise and the pads floated up to his chin and he looked like a turtle sticking his head out of his shell.
The suit lasted us for 2 long summers and I feel it really helped my child to get a feel for the water and learn to use his arms and his legs to move around the pool. The suit should be used with caution though because a child left unattended wearing it, could have some problems if they flipped face down.