This might help you - or anyone else dealing with hearing impairment and a mask.
For those who don’t want to watch, it’s a demonstration/suggestion by an NHS ambulance driver - use Google Live Transcribe on your phone. It’s probably already installed if you have an Android phone, and is available for I-things as well.
I’ll certainly keep it in mind for the next time I deal with a hearing-impaired customer at work, mask or no.