If you love the look, I would invest instead in a teak shower bench/ stool that you can change out when / if the wood deteriorates rather than building it in. Also, with all white / gray / blue, I'm not seeing that the wood element is best in the shower.

Teak and ipe are the only woods that will hold up in a shower. You could have a seat / bench fabricated out of solid surfacing (Corian. Zodiaq, etc.).

Total agree with Libra about using a separate bench and just plan to replace periodically. I figure it has to work like teak outdoor furniture in that you need to keep it oiled and it will eventually look gross. You could also try a wood shower mat to bring in the wood look that you want.

You can use a sealer on the teAk. A lot of my clients have moved to the portable benches instead of fixed ones cause they can place them where they need them & adds texture to the shower. I'm gonna do that myself whenever we get around to doing our own!!!