What a nice idea to buy a lasting souvenir in Paris!
The great French jewellery houses are (in alpha order):
Boucheron, Cartier, Chaumet, Poiray. All clustered on the fabulous Place Vendôme.
With the price of gold today, for about €850, you’ll probably be limited to a ring. Try Poiray for the most reasonable prices. The French don’t make jewellery in 14K gold, as it is not considered a fine metal, by law.
On the second-hand market, you could try Collector Square (they have a website), for perhaps a Cartier rolling Trinity ring. They have a good reputation for selling authentic pieces.
Enjoy your trip!
