You can buy something called water soluble canvas, which has the cross stitch grid. In my country I have only found 14 count.

I recommend basting it on, and then starting in the middel so it don't shift while you stitch.
When you are done you just wash it.
I have made these pants using that

There is also something called waste canvas which you pull out after you are done stitching. But I don't have personal experience with that.