Bachelors thesis on my desired topic already written by previous years students There really is only one topic that I find interesting, useful and that I have alot of knowledge of. However students of previous years had already chosen this topic and written Bachelors thesis on it.

How bad would it be if at least half of my thesis was already researched in previous years thesis?
Unlike dissertations, bachelor’s theses need not be on an original topic or advance the frontiers of knowledge (although those goals are desirable!). A bachelor’s thesis is intended to show that the student is capable of synthesizing information to produce a useful result via research in some form or another.

So unless the school has a requirement that topics cannot be repeated, there is no reason why you shouldn’t be able to produce a work on a similar topic. That said, your work should not be identical to the previous work (which you should cite and discuss in your thesis!)