IMO 3 options …
LevelSpeech2.ny plugin for Audacity,
Audacity’s envelope tool (a manual process, so slow, but capable of the highest precision),
Free Standalone software called Levelator.
The dynamic-range-compression used in Levelling plugins may increase sibilance to unacceptable levels.
then you’ll need to de-ess, e.g. with desibilator plugin.
