ACS are your friends. They’re moulded earplugs to your own ear-canals (I got mine done at Boots). I’ve got their PRO17s which apparently give the flattest most neutral sound, no particular frequencies dropped over others.
In the band I use them for the music drops from intolerably loud to that of the sort of volume you’d listen to music at home, every instrument crystal clear - in fact it’s a better sound than without them as being quieter it’s far easier to focus on the rest of the band.
Not cheap - about £150 - but what price is our hearing. Not IEMs by the way, just regular plugs.