I would definitely not use rope alone for bondage as rope bondage carries many risks, not all immediately obvious. The safe option is to use leather wrist and ankle cuffs and maybe use ribbons initially looped through the rings in the cuffs, then maybe move to rope but again used through the rings in the cuffs. Another option is an under bed bondage set (plenty on Ebay) much safer than rope alone.
Don't be tempted to use handcuffs, quality or cheap, as handcuffs are risky, as well as mislaying the key they can hurt, or cause damage because they are thin metal and can cut into the wrist or ankles, whereas a wide leather strap cuff is soft and spreads the load.
Don't do bondage involving the neck, that's very risky.
Sex, with a little kink, or full on kinky sex or BDSM with or without sex is full of risks that are not always obvious, you need to learn before you continue. Take a pause and learn, learning will increase the range of options you have for play, but the main reason to learn is to avoid seriously hurting your current girlfriend and future ones. To be safe in what you do.
There is lots of good information online, on You Tube and in books to get you started, but as well as that information you should go to workshops run by experienced BDSM educators and peer to peer teaching groups and learn how to do this safely.
Please take a pause. I know you might be thinking, nothing bad has happened so far, what is this dude talking about, but believe me BDSM and Kink is very, very dangerous. You have been lucky so far.
As a start read the Loving Dominant by John & Warren, Libby Warren,
also Screw the Roses Send Me the Thorns by Molly Devon and Phillip Miller.
Read the Dominant Guide website
http://dominantguide.com/
and the submissives Guide
https://submissiveguide.com/
Morgan Thorne's You Tube channel is good for practical demo/teaching information
https://www.youtube.com/channel/UCwx8uy7nxohWLwnaPocLsyg
Also Evie Lupines You Tube channel is very useful
https://www.youtube.com/channel/UCHExB-d5s0zBcbsaHEUy91Q
Welcome to the Cage, the world of Kink and I wish you the best on your journey.