Problems with disappearing voice

Hi all,
My husband was diagnosed with Parkinson’s six years ago, although is now thought to have Dementia with Lewy Bodies. Physically he’s not in bad shape (he’s 68) but cognitively he struggles. Over the past couple of years his voice on occasion is barely above a whisper, and this is now increasingly becoming the norm. Therapies that encourage you to THINK LOUD! and thereby project your voice don’t really work due to the cognitive challenges. The speech therapist suggested either sticking an earpiece from headphones in one ear and play white noise, or obtain an amplifier to wear around his neck. The first doesn’t work and I’ve yet to resort to the second. I know in the US there is an app being developed to help with this problem and that there’s a sophisticated version of the white noise idea available over there called SpeechVive (anybody got this?). Just wondering is anybody else has experience of this and can offer some useful tips or suggestions? My hearing isn’t great at the best of times so it’s frustrating all round. Cheers.