if you want to do shorting with bitcoin probably binance will be the good option since they have futures trading for shorting and good leverage as well but it requires an amount to avail such features mate.
Binance.com or Binance.us?
US citizens can not trade on Binance.com
Binance.us do not support future or any other means of leverage trading.
If i remember it correctly you need significant amount something like that for each leverage.
Significant amount of what? Hope not money? Traders should trade with the amount they can afford to lose.