There are more styles of cardstock with more finishes than you think. I’m sure there’s something good out there.
Here’s a crazy idea too: a really nice print of whatever image you want as your underlayer. You can make your own printed ocean image and go from there. If you dont want to do that, find a nice wrapping paper or premade printed cardstock and go with that. Several people have used very pretty origami papers as backings to similar effect… here’s one from @monosyth
Nothing chintzy about using cool mixed materials.