Firstly If you believe that plastic bottles are bad for human health then the best way to overcome your worries is to stop using them completely. There are good quality bottles with no BPA and have food grade plastic which is very important - not just for you but for the nformation of the general public at large. Such bottles are mcuh safer than many. Secondly, On my personal research, I have not found even a single scholarly article about stevia
in any reputed medical journal. As a doctor, in view of no scientific data to back up this compound - I will suggest you to avoid it compeletely.