Financial futures might be the easiest to understand. Look into the S&P emini future. Don't do any trades until you understand the contract and have a strategy that show promise. What have you traded up to now and how have you done?
It's not for me, but for a person who says it is successful with stocks and needs better leverage, but not with big automattic trading from big firms.
It would be easier to suggest a future if I knew your general strategy and risk profile. ES contracts are on the low side of volatility vs most futures. What are you looking for?
If your friend is already trading stocks successfully and wants to move into futures, he/she can either a) trade a futures contract not strongly correlated to the market, for example crude oil (definitely NOT a beginner's contract!), or b) trade stock index futures which is no different than trading SPY or QQQ but with more leverage, and would require little if no adjustment. Your friend is going to have to adapt their trading plan, however, because if he/she trades just the index futures for example, there will be fewer opportunities than if they're used to tackling a basket of stocks.
Why is this guy researching for his friend who supposedly is already doing well with stocks? Why isn't the "friend" on here asking for advice? Something is fishy about this post/poster. I smell BS
Who cares? Even if OP has absolutely zero idea of how to trade and is about to plunge their savings into the ground, the forum is a knowledge repository so there's no harm done putting out the correct information, don't you think?