I hope it's not too late to respond to this.
If you are planning to stay primarily in hostels, you may find that you don't need to set up a specific travel partner for your whole trip. You may find temporary travel partners along the way.
I traveled solo on my first trip to Europe. I found that it was easy to meet people to share information about our adventures and maybe go on some together. It was a very long time ago, but I think it is probably easier to do now than it was then. The hostels are nicer and communication methods are easier.
I was 30 at the time, a bit old for hosteling back then, but you are a prime age for doing it. And these days hostels have all ages and backgrounds staying there. When I went, there was no Schengen, no Euro, no cell phones. I traveled for 4 months in the fall and winter, going the opposite direction you are going. It was all good.
These are some examples that I believe would not have happened if I had been traveling with a partner:
In Florence I ran into an Australian woman who I originally met at the hostel in Bath. We decided to go to Rome together for Christmas and rent a pension room. On the train to Rome, we met an Italian guy who told us how to get the best place to stand (no seating available at that late date) for Midnight Mass at St. Peter's. We followed his instructions and it worked out great. Then we were each on to our next stops.
I met a Danish woman in a pub in London. She was heading back home but her parents were gone for several weeks, so she set me up to stay in their apartment in Copenhagen for free when I got there.
I met an English woman in Spain who invited me to stay with her in London toward the end of my trip. I took her up on it and it was the perfect place for me before I flew home.
On the trains, I ran into other young travelers from all over the world and we often got together to find a place to stay. My best story about that involves an old Spanish gentleman who was at the train station in Barcelona looking for guests for what I assume was the pension of a friend. He guided us to it.
He spoke a little English and I was the only one who spoke any Spanish. I'm sure he was getting some money from the pension owner for bringing in customers, but I tipped him anyway. Just about the time we were settled in, he came to the pension and invited us all out to dinner -- his treat! Why? He took my tip, played the lottery and won a lot of money.
I tell these stories because sometimes traveling alone can lead to adventures that being focused on another person will prevent. And the concerns about setting up a long-term "relationship" with a stranger that others have expressed are legitimate. I'm sure there are many more uncomfortable situations that others could talk about.
The only one I know about sort of personally is that my cousin went with her best friend and after they got to Europe, it turned out that all the friend wanted to do was shop. She had lots of money. My cousin didn't, but even if she had not been doing the trip on shoestring, she still would have avoided shopping because she had other interests. So they had breakfast in the morning, split up during the day and got back together in the evening. My cousin thought they would share the European experience together, but it obviously didn't work out quite that way.
My recommendation is that you not feel like you have to have a travel partner. You can go alone. If you do find a travel partner, you both need to be very upfront on your expectations and how you will handle it if things start going off the rails.