The Sea Side by Notos has an area in the beach, with chairs and beds to spend the day. There, you'll find 3 boys working in the beach - "Lefty", Kostas and George - they will bring you everything you need.
In the restaurant, Peter makes the hosts, being a very professional and friendly staff and restaurant coordinator, in a place where the food is AMAZING. A must go and a must stay during your Santorini trip. ;) and you find wifi in the restaurant and beach.