Mouldable wax and silicone ear plugs are the number one choice when it comes to comfort. They sit over the ear canal, rather than inside it, and will fit any size of ear as they are mouldable. Mouldable wax and silicone ear plugs are a great choice for sleeping because of how comfortable they are to wear- they don't protrude from the ear meaning you won't be in discomfort even when sleeping on your side.
In addition to sleep, they're also suitable for study, concentration, relaxation, and general hearing protection in mildly noisy environments. They're also a good choice for swimming and other water-based use, but you should generally avoid using them in hot water.