How to be sustainable when changing styles?

Hello! Im a teen that is trying desperately to be more eco friendly. I have never paid attention to style and just got whatever average Joe shirt that was on sale. Now, I really found my style and I yearn for it a lot.

My original plan was to donate all the clothes I wont use and keep some for art. Then I would thrift my new style, but after some research, that still feels pretty wasteful.

Any ideas on ways I can change styles sustainability? Or if not, some ways to mend and change the cloths I have now without having to but expensive materials and research?

Thanks!