Watches with no metal

[Spikeytree]

Anyone got any ideas? I want to buy my DSis a watch for Christmas but she is badly allergic to metals, so it needs to not have a metal back that will be in contact with her skin. Under £100 if possible.

All ideas gratefully received, I'm really struggling to find anything. Thank you.

Swatch watches used to be very plasticky. Not sure if the back is included though.

Thank you, I think I may have found a nice one on the swatch website. As far as I can see the back is plastic too, so it should work.