I also prefer to book a cabin by myself because even with a friendly easy going roomie..... it is too crowded to walk around in the cabin unless you get a balcony cabin.
I am willing to book a insider which is cheaper but still cost more than having a roomie but it is worth every dollar spent. I have done it once already and I love it. I have already booked my deposit for a single suppliment again with VTG singles. BUT.... if one of my friends needs a roomie really bad I will share a cabin with them because they are my friends.