Our books do lay flat for viewing, so they look great with double page spreads.

To set these up, you'll start with a page sized at twice the width of the book size, so an 8x10 book would start with a 16x10 page.   Once you have completed the layout, then you'll split that spread into the left and right sides and save the individual Jpg images.  You can then upload those files, and they should line up perfectly online.

One note, while you don't lose any of the image in the center fold, I'd still caution against placing anything mission critical in the center, like a face or text.   Placing something like that in the center can be a distracting design element.