Yes, should you be flying Business Class to Johannesburg, then many airlines offer the option to use streaming apps during the flight, which is a great way to catch up on your favourite TV show. For example, flights with Virgin Atlantic offer this as an option for a set fee.
At Heathrow Airport you can access several lounges depending on which airline you fly with. Should you be flying with British Airways the you can use their North Club Lounge for free. This will provide you with complimentary food and refreshments as well as facilities where you can take a shower. You could also use Virgin Clubhouse lounge if you are flying with Virgin Atlantic, which has a games room and an al a carte menu.
Airlines that offer Business Class flights to Johannesburg tend to provide a great service on board. One airline that is considered to offer a superior experience is Virgin Atlantic, which offers lounge access as well as advanced seat selection before you fly. Whilst in the air you get lie-flat seats, charging points for your laptop and a dedicated bin space.