I have seen this question pop up on here and there's a simple solution to avoid copy/pasting and re-editing your Medium posts.
First of all you need to install node on your computer.
There is an installer for node for all platforms, just download it and install it like you would any other program:
Once you have this installed you fire up the Command Prompt on Windows or Terminal on MacOS or Linux and run this command.
npm install -g mediumexporter
This installs mediumexporter. Once installed you can export your Medium post to markdown format.
Go to the directory where you want to file to be exported to. For example c:\Users(username)\Desktop on WIndows or on Mac:
cd c:\Users(username)\Desktop (on Windows)
cd ~/Desktop (on Mac)
Next type:
mediumexporter https://medium.com/@xdamman/my-10-day-meditation-retreat-in-silence-71abda54940e > medium_post.md
You'll see a file called medium_post.md containing your Medium post in markdown format, which you can copy paste into steemit with all the formatting intact. You might have to adjust a couple of things but most of the time it's fairly good in preserving formatting and structure.