Help visibility for swimmer

I received this email from someone and I wonder if anyone would help out with an answer??? I usually wear a bright colored home made fabric waterpolo type cap when swimming along the shoreline. I never swim alone. re: swim buoy I am looking for a streamlined buoy that can be towed behind an open-water swimmer to assist others on shore or in boats to see the swimmer. In this case, my mother, now 80, swims about a mile a day. She enjoys going to the ocean in the Caribbean and swimming out and back, quite a ways. Were she to use a tow buoy, and/or a form-fitting life vest with a depth-sensitive inflating device would provide family members more comfort. When I have been there, I kayak alongside. I'd be grateful for your advice.