I wear foam earplugs every night and when inserted properly, they attenuate probably 98% of ambient sounds in my environment. I have to have my phone alarm set to a specific alarm that apparently pierces that barrier and effectively wakes me up. Otherwise, road noises, AC hum, clocks ticking–absolute zero.
I have two specific ones that work well–I think comfort being a very important factor, too, because they are almost completely inside my ear canals. I use either Laser Lite NRR 32s (Howard Leight “brand”) or Mack’s “Ultra soft” with NRR 32. Walgreen’s store brand clone of the Mack’s work well, too. They’re likely the same thing anyway.
To me, there are two ways you can reduce what you hear when wearing earplugs. First is to make sure they fit and are inserted absolutely correctly. If your ear canals are too large, the foam ones won’t expand enough to block enough sound. The other way is to find an earplug design that works sort of by baffles and then some small amount of suction. By that I mean, there are earplugs that have several circles of baffles. If you put those in (again, nice and tight in the eardrum), and then pull on the stem ever so slightly, that has the effect of creating a negative pressure space between the eardrum and the earplug, essentially completely preventing the eardrum from moving except for very low frequencies. I have used the latter type in very loud industrial environments with great success, but but they are NOT comfortable for sleeping, I’ve found.
Hope this helps.