Bachelor thesis: cite my own paper?
When it comes to copy and paste, I'd certainly have a bad feeling. Paraphrasing/rewriting is the least you can do. In general, citing own publications is common practice. Citing your own publication in your bachelor thesis is therefore, in my opinion, completely okay. 

Since the research published in your paper is actually part of your thesis, everything should be fine. But in your thesis you should be able to give even more detail than in a conference paper. That way you can reference your paper, showing that you published successfully, and then show your findings to a bigger extent.

Good luck with your thesis!

Edit: Almost forgot about your first advisor: Talk to him/her! There is no reason to feel bad for asking. Ask your second advisor for advice on how to talk to your first advisor.