If you already know that you can't use foam earplugs, then perhaps it's time to try silicone putty. Soft and pliable, the silicone moulds to your ears for a unique fit.
Silicone earplugs are waterproof, reduce noise by around 22dB and best of all, they're very comfortable. They don't go into the ear canal, but stick gently across the opening to it.