We tried everything. The only thing that worked was to have an adult hang on to the kiddo while underway.
There are a bunch of life vests for the little ones. I looked for you, but the place we got them is now out of business. I did a search and found nothing....but the name of the life jacket we got was called "kiddie care" and it held the head out of the water even in the chop.
A kids tube for playing and a pair of tightly stretched nylons made a great shock-absorbing bed for the deck. If you had to bail this, combined with the life jacket, would keep the little one right out of the water.
I dont think you are even close to over protective. You sound like you are prepared to me.