Just a couple of more points, not to argue, just for thought.

On my last pool I used 1 1/2" styrafoam 4 x 8 sheets. I had them on hand and wanted to use them for something. I liked the end result very much. The bottom was just a little softer than sand and there were never any footprints or cracks. Thickness may be a factor there.

In many cases sand can lead to lots and lots of footprints. I am talking about a good sand installation. Without wrinkles and footprints. Not everyone can do that so other options may be better for you.

One thing I can say about sand compared to any other types of base. If you do get wrinkles in the bottom sand is the easiest base to smooth them out and make the liner look presentable. With a harder surface wrinkles can become a nightmare.

Best of luck, Dennis