Just buy something that you like or your partner would like.
The jewelry industry suggests two-month salary as the rule of thumb. However, having been through, I would say don't go crazy with it. It is a symbol, not an investment.
As for where, one of my colleagues (a gweilo) likes to buy diamond from Alaska, usually on cruise ship trip. His wife likes collecting stones and they can afford this expensive hobby. He said the price is much better and skip the CRA's cut ;-)