Actually most women dress much better on the street than in a gym. If you believe otherwise, perhaps you should worry that when you go “outside” you are hading to places where people are especially disreputable.
It would be good if a frum entrepreneur could make a go of single gender gyms, and related videos. Books are less of a problem.
I’m not sure if the rules on underdressed females apply if the pictures show them not only without clothes, but also without skin (in some exercise books this is done to illustrate the muscles).