If your television has "line level" outputs - two RCA jacks, one red, one white - you want to find a headphone transmitter unit that accepts this type of input with the matching input jacks.

Televisions that only have a 1/8" mini-jack headphone connector usually have internal contacts that disable the internal speakers when they have a plug inserted.

By the way, I'm assuming you are looking at wireless headphones here that have a separate transmitter and then of course, wireless headphones, to listen to the program.

Your cable or satelite box may also have RCA connections for audio that can be used for input to a wireless haedset transmitter.
I have an inexpensive Sylvania headset (I can't find a model number) that can receive radio or the TV audio.

My spouse uses a little hearing aid like thing, looks like a blackberry ear piece but costs less than $50. I cannot find it online now. I will look and get back.

Micro Plus - Harriet Carter - Health & Beauty > Therapeutic Aids is the gadget my wife uses. She uses it only for TV at home. She says she would not want to use it up and around, at work or the like.

I walk by the audiology dept at Costco often enough, and they carry some gizmo. Don't know details or cost, tho. So check with a hearing-aid shop.