HEADPHONES!!!!
Absolutely one of the top recommendations I have, and with very good response from those who have used them, is getting wireless headphones.
A crowd favorite is the Sennheiser RS120 series. They aren't audiophile grade, they are just good at doing their job for a very good price. There are certainly better options out there, and you may want a set with a digital audio input, but that'll run you a bit more cash.
At the end of the day, a soundbar is better than internal speakers, as separate speakers/receiver are better than most soundbars. But, when people are hard of hearing, one of the best things you can give them is headphones. They can individually adjust their volume and it works for movies, music, and just watching TV. This is especially helpful at midnight when others may be trying to sleep in the home.
I have at least half a dozen clients who have added headphones to their viewing habit.