There are latex foam mattresses. I've purchased two from Sleep on Latex (sleeponlatex.com, or Pure Green on Amazon).
That said, whether latex, polyurethane, or whatever, with foam mattresses you're supposed to use a mattress protector to prevent sweat and accidents from soiling the foam. Alternatively or in addition to that, Sleep on Latex uses a wool topper, as I'm sure many other brands do. And then on top of that most people use sheets. I would think all of that covering would trap any particles so they can conveniently be washed out to sea with all the other microplastics from the laundry.
That said, whether latex, polyurethane, or whatever, with foam mattresses you're supposed to use a mattress protector to prevent sweat and accidents from soiling the foam. Alternatively or in addition to that, Sleep on Latex uses a wool topper, as I'm sure many other brands do. And then on top of that most people use sheets. I would think all of that covering would trap any particles so they can conveniently be washed out to sea with all the other microplastics from the laundry.