White gold is usually yellow gold that is plated, so doesn't stay "silver" coloured over time. I wouldn't buy white gold for that reason.
I would probably invest in some diamond studs, a diamond ring or something fabulous in sterling silver. Silver can be cleaned up beautifully although it's a softer metal of course than gold. Probably the best metal is platinum as it's the silver colour you want through and through, and it's very hard, (harder than gold/white gold or silver). You can get platinum and diamond rings for £1000 or under if you look on the internet.
Although second-hand is good, I personally equally like just buying a ready-made piece direct from a jeweller. If I like a piece, it's pretty and I love it (and will wear it) then I'm personally not bothered about "getting more bang for my bucks" and all that, squeezing out maybe £1250 of product from £1000. Sometimes it's nice to have the experience of just going and choosing something from a jewellers rather than searching the second hand places looking for more of a bargain etc. (Each to their own though.)
Also, they don't seem to be that popular on here because they aren't second hand, or custom made, and people moan about the mark-up for the brand, or a kind of reverse snobbery, but I think many Tiffany pieces are gorgeous and very well made. Tiffany is classic and iconic and holds its value well because it is a brand, unlike generic jewellers unless the quality of the stones and the metals is extremely good. Tiffany also have a polish and restore service I believe.