We are looking for a hotel on the south coast of France betweenSt. Tropez and Hyeres. We would like it to be on the beach.
We stayed at a nice little hotel on a sandy beach, which could fit the bill for you. It's the Hôtel de la Plage, minutes from Le Lavandou on Aiguebelle beach. Bormes-les-Mimosas is a lovely village to visit and have a meal in, just a few minutes from there in the hills above the coast.
It is available through booking.com, but if your dates don't show available, check with the hotel directly. I know that they have at least a two-bedroom set-up that they don't list.
We enjoyed our stay here and even went swimming in mid-May - the water was a bit cold, but the place was very quiet and relaxing. There's a nice set-up with beach chairs, for sunning and reading. In the summer months, this place is very popular (mostly French, German and other European tourists), so given how the balcony seaview rooms give onto the sea-facing courtyard with the bar - it would definitely get noisy.
There aren't many nice sandy beaches along the coast, most being pebbly.