My daughter is 4 1/2 years old, been learning to swim for almost a year now. She has slowly gotten over her fear of the water. I am ALWAYS in the water with her and if she wants to try something I let her with me always there able to get her if she panics.
The one thing my daughter loves is a blow up innertub that she is in, she lays on her stomach with her body/legs through the hole in the water with top/head/arms out of the top. She can easily move around kicking and is learning to steer with her legs and arms. NOW she did flip, paniced but I was right there to pull her up to the surface. She was scared but I calmed her down and we kept on swimming.
Kickboards are also go to help him yet give him the independence he desires. Floating chair that is very stable and would be hard to tip (not the blow up kind), to relax in the water, so still in the water but a little rest time to get energy back to keep swimming.
Swimtoys... pool squirt tubes, diving rings (or similar), could just go to the walmart or target summer/water/pool aisle and have him pick out 2-3 cheap toys that he is intrested in.