For a simple airport transfer, use National Express coaches from Victoria Coach Station to Gatwick

https://www.scribd.com/document/1077066259/Heathrow-to-Gatwick-Airport-Transfers-Coach-Taxi-or-Train-174457

For a simple airport transfer, use National Express coaches from Victoria Coach Station to Gatwick. They’re reliable, have luggage space, and can be cheaper than trains at off-peak times.