The Legend entries will be the same as the command. I suggest rather than creating a second plot, try copying your commands. (select then command-C to copy and command-V to paste.)
In the copies, increase the line thickness and check ‘Hide’ so you only see the thinner lines, but the thicker line still shows in the Legend. Here the copies are 4 times the pen size.
This will show up as one entry in the Legend since they have the same name, but you will see the command with the thicker line.