What type of ear plugs are best for sleeping?

Personalize. So long as you don't have issues with otitis externa (outer ear infections) any type should be fine. Try the foam ones but, make sure to check them daily to make sure they're intact; you don't want one to break up in your ear canal because you've used it for too long. If those aren't your bag, go for the wax ones. If that fails, see an ENT for customized ear plugs.