I recently moved from Cura to Simplify3D and one of the things I really missed was the ability to upload and start a printing job directly from the slicer UI.
This is not directly supported, but Simplify3D can execute a script to post process the generated gcode file. There you can tell Simplify3D to upload and print the genearted gcode file.
You need to have cURL installed in your system. This already comes out of the box on macOS and most Linux distributions. Check this guide out to install cURL on Windows.
Once installed, edit your printed profile by editing a Process, and on the Scripts tab, under “Post processing”, input the following:
curl -k -H "X-Api-Key: YOUR_API_KEY" -F "select=true" -F "print=true" -F "file=@[output_filepath]" "http://OCTOPRINT_IP/api/files/local" {STRIP "; postProcessing"}