I was referring to the .co version but even then, after searching, I found a decent amount of scam accusations, so If you're planning to use them for real transactions, you should be careful.
Since you are not sure of the recommended exchange, its best it goes off the list of platform to be considered entirely so he doesnt fall victim of fraud and end up blaming you for it, the bitmex you have recommended is still the best for now for a beginner, it is safer to use than other exchanges, though we have some exchanges too that has been in existence for long and safe, but still, I will recommend bitmex or Binance for a safe trade for real trading and transactions!
Hey OP, this is the list what exactly you are looking for. Out of them, etoro is having another wonderful feature of social trading. With that feature you can "copy" trade of other experts. When I checked last time, it was not free and not sure about current status of its cost and accuracy. Trade with extreme caution and responsibility.