OK, definition of decibel is the faintest sound a young sensitive ear can hear. So that means zero across the board is perfect human hearing.
"Normal" hearing is generally the -10 to 15 db range. (There is no absolute standard.) "Slight hearing loss" is 15 to 25. "Mild hearing loss" is 26 to 40 db. "Moderate hearing loss" is 41 to 55 db.
When you first had your hearing tested, it would be called a 45 db loss in the right ear, 42 in your left ear. (Average of 500, 1000, 2000, and 3000 hz readings.) That's in the "moderate" hearing loss range. Now it is 35 in the right ear, 36 in the left ear, or the upper part of the "mild" range.
Various hearing aid sites will tell you which range they are most appropriate for. Many are marketed to just that range ("mild" or "moderate.")