Life / Where in Warsaw would be a good place to buy an engagement ring?? [5]

I've been living in Poland for a little over a year and I've been going out with my girlfriend for over 3 years and it's time to propose.

However I wondered if anyone might have advice about where in Warsaw might be a good place to buy a ring? Like the big jewellery shops in Zlote Terasy or Galeria Mokotow? Or are they probably overpriced? Has anyone had good experiences with buying jewellery in Warsaw or advice that they can share?

Thanks.