Designing Kitchens and Bathrooms - wood floors

We just bought an old house and the main bathroom has carpet, then old linoleum (?) tiles and then nice oak. Rather than spending the money on re-tiling the floor, we are tempted to go with the oak, as it would look terrific with the rest of the bathroom and house. But, we are worried that water will damage them and even make its way down to the downstair ceilings.

Right now it is just the two of us in and out of the tub. But there will be kids one day. I hear that a thick coat of polyeurthane could do the trick - as well as a slab of marble under the base of the toilet. Any thoughts? Too big of a risk?

Thanks!