If you have your own music collection, I can really recommend normalising everything to a LUFS value of your choosing. (A common value is -14 LUFS for most streaming services Source)

Note there are two types of normalising, dynamic and linear. Linear is what you want as it’ll only move the average loudness to your target, preserving the difference between the quietest and loudest parts. Dynamic normalization squashes the quietest and loudest parts into a narrower range.