I live and dive in DR for the last 25 years . We do have plenty of locations with clear water and white sand , water temp at this time is 26-27 celsius.
I can give you some guidance based on what you want to do exactly and your budget. Island is quite big so i suggest to plan ahead first and then choose to fly to the airport here that is closer to your chosen location . Airports options could be La Romana, Punta Cana , Santo Domingo , Puerto Plata and El Catey ( close to Samana ) , all international airports with daily flights from USA except El Catey which i'm not sure if only receive charter flights . All of them are close to white sand beaches with clear water.
Any additional info let me know