Netflix doesn't have much, but if you have a Roku there's probably a dozen or more fitness channels, and most are free. Quality varies, and some of the free channels run ads before every video - and on some channels the videos are only a few minutes long.
Try Fitness Blender on youtube. They have a variety of workout videos tailored to individual needs. You can program a playlist of the vids you want to use, then bring them up on your TV with the youtube app. Works pretty well and it's free. There are a bazillion other workout vids you can choose from if you don't like Fitness Blender.