exchange – How to trade bitcoin in bitcoin?

I'm curious about how to trade bitcoins for bitcoins. I want to do this because it measures the gains (and losses) of crypto. I do not intend to do this with leverage for security reasons. So what I mean is (but don't say that) Bit-MEX (for the most part): the price doubles and the amount in real dollars quadruples. This amounts to negotiating with leverage x times where x is the current price divided by the entry price with negligible or no liquidation risk. I would prefer it to be for Coinbase because that is what is popular.

Example based on previous data:

The price of BTC was $ 3,150 in December 2018 … 0.05 BTC bought for less than $ 200.

The price of BTC is $ 13,400 in June 2019 … 0.21 BTC sold with ~ $ 2,750 in return.

Note: Don't tell me to use Bit-MEX, Bitfinex, etc. because I live in the United States.