You can get what you want at Koh Samet and Koh Samui but I'm not sure about Hua Hin, unless you stay in one of the upmarket hotels, but certainly at Samet & Samui you can have a bungalow right on the beach sand. Perhaps if you name the hotels/bungalows you have booked someone will be able to tell you if you'll be right on the sand. Many beachside places in Thailand actually have a road between the hotel & the beach.