I think a combination of different quality of marks often creates a more interesting print.
Foam plate relief printing often creates solid white line kind of mark. You can create variety in the line quality by drawing the plates with different kinds of tools.
In the print above I used a pen, pen cap and found weeds to make the foam plates on the left. But to create the bolder marks on the right I combined a solid plate with “masking stencils.” I used plant material for the lower right image and cut paper stencils to create the shapes on the upper right side.
Masking stencils like those shown above are not usually used in relief printing. But if they are super flat they can be combined with a plain unmarked foam plate with pleasing results.
I thought of this combination of materials, because as a gelatin printmaker I have stacks and stacks of masking stencils.
So as you work on creating your mixed media prints be open to combining processes and materials in new and unconventional ways.