I would say a pair of ear protectors that have good filters built in so that you still can hear the higher frequencies. There are both standard models and custom made (from ear impressions) available on the market
I have some of them already. I love them to use. But everyday new earplug is coming in the market. So I need different one all the time. LOL!
Personally i am using 3M Peltor H6A/V Optime Earmuff,It work as an aircraft mechanic in a high-operations tempo environment... meaning I do a lot of running around, a lot of tumbling around, and get a lot of jets fixed to do a lot of flying. I've used numerous other forms of hearing protection which makes it best ear muffs for sleeping: Peltor Shotgunners, Peltor H10 Optime, Bilsom Thunder, from what I can recall.