If you match the tv's resolution, you'll be fine. I created a museum exhibit that was on a ~46" tv whose native resolution was 1024 x 768 and it matched perfectly.
If you are using it as an actual TV then as was said before, you would want to set it to the native resolution of the television. In the US all televisions conform to the ATSC (atsc.org) standards. For an HD TV you would probably be dealing with a size of either 1920 x 1080 or 1280 x 720.
If yo are just using it as a computer monitor though you would want to set the document size match the screen resolution that you plan on using. That will actually have a lot more variation in sizes.