There are many options available but the one I use for myself, and my clients , is the Original Boot Shaper.
In my opinion they are good quality, easy to use and keep the shape of the boot. If you store your tall boots on a shelf these inserts are hidden in the boots so they look neat and organized. They also come with a integrated hook if you prefer to hang your boots.
Right now they are on sale at The Container Store so it is a good time to stock up!
Functional, good price and look great (because you can’t see them) is a winner in my book.