I am in the middle of writing my bachelor thesis and recently submitted a paper that I wrote with my supervisor about the same subject to a conference. If it makes any difference, I should mention that I am the first author. I would like to use the paper (15 pages) as the basis for my thesis (about 40 pages), i.e. I want to re-use most of its content without changing the wordings.
My supervisor told me that it is okay and I have read that it is even common practice among some institutions to reuse your own previous work for a bachelor, master or PhD thesis.
However, I am not quite sure if it is acceptable to reuse paragraphs which my supervisor wrote as co-author to that paper. In the Statutory Declaration that has to be attached to the thesis it is stated that I wrote the thesis just by myself with only the help of the cited material. Do I have to reformulate the ideas in this case?