What should a student look for in an undergraduate thesis supervisor?
I would recommend you to take to things into consideration:
First, find a topic that you are interested in and motivated to work on. And then, try to find profs in your department that work on topics similar to what you plan to work on.
Second, try to figure out how you would like to work (and this is very important).
If you feel confident working more independently, the supervisor won't play a significant role there. If you feel that you need closer guidance, try to find a supervisor that is willing to do that.
Now, it is important to note that you will likely have to compromise some of your needs. It is possible that there won't be many professors willing to supervise you on a topic you want rather than what they want and will recommend you to join his projects/topics. On the other hand, you may find someone willing to supervise you on the topic you choose but won't provide you with close support.
Back in my undergrad thesis, I had a topic I really wanted to work with and only had one prof on the field to supervise me. I had very minimal supervision.
Was it the way I wished? No. I could've gone farther if we had worked closely and if I had had someone to discuss with or to push me.
Was it worthwhile? Definitely! This has brought me independence, which prepared me for many of the challenges I had throughout my masters and Ph.D.