Another choice for flexible printing is polypropylene. It is possible to print polyp on most simple machines - I have don quite a lot using an unmodified Ender 3 pro, the only problem has been print bed adhesion. Polyp pretty much only sticks to more polyp but when i've tried to print it onto Polyp sheet it has welded itself down irremovably so had to resort to printing onto polyp packaging tape applied to a glass substrate.