If you've got some money, get custom molded earplugs made for sleeping. Places selling hearing aids sell them. They spray some foam in your ear to take the print, and you get the custom plugs in the mail a few weeks later. €140 is a lot for earplugs but it's amazing that they just slot into place in your ear, they're easy to pull out, and they're so small you don't feel them wether you're lying on them or wear headphones over them.