Rachael, you have another potential problem to consider. Sooner or later, you will get water under the feet which will lead to black stains on the floor and then to rotted wood. Poly will not stop water, as so many questions on the board about white and black stains indicate.
I am not wild about any hardwood floors in bathrooms for that reason. I have one thought that might or might not work but, because it would be pretty "experimental" I would not try it without a lot of agreement here or comments from John Leeke at www.historichomeworks.com. You might want to contact John and see what he has to say first. His e-mail is JohnLeeke@ historichomeworks.com.