Now that Barry has found out how to leave sound playing through the TV's speakers, even though there are headphones plugged into the socket, I'll offer you the solution which another ABer with hearing difficulties (Jennyjoan) uses. That's to use a good-quality set of wireless headphones.
Jennyjoan uses these and I know that she's very pleased with them:
https://www.currys.co.uk/gbuk/audio-and-headphones/headphones/headphones/sony-mdr-rf811rk-wireless-headphones-black-22095633-pdt.html
To use those headphones, you simply plug the transmitter unit into the TV's headphone socket. The person wearing the headphones can then hear the audio anywhere in the house, with a volume control fitted on the right-hand earpiece. The sound quality is excellent and the headphones are so comfy that it's easy to forget that you're wearing them. The headphones are charged by plugging in a lead from the transmitter unit, with a full charge lasting around 13 hours. (They can simply be left on charge whenever they're not in use).
I also use those headphones (and recommended them to Jennyjoan), as do several other AB members (including Woodelf).