Looking for a small apartment in Cologne

Hi everyone!
My name is Magdalena Casset, I'm 25 years old, and I am from Argentina. I'm looking for an apartment for two persons (for me and my boyfriend Tomás).
My boyfriend and I are college students in Argentina but we decided to pause our studies for a year to apply for a working holiday visa in Germany. We are both passionate about traveling and this is the best way for us to do so, while being able to live and work in a community different from ours and learning about the country's culture (and hopefully we learn the language too!).
So currently we are looking for a small apartment that allows us to carry out the registration. If possible, we are searching for a long-term rent (although we are open for a short-term one). My boyfriend is going to arrive in Cologne 3 weeks before I do, but we are still looking for something for both of us from the beginning.
Any information or questions you may have are welcomed!
Thank you for your time,
Magdalena and Tomás.