Could always make your own if you have a 'fill yourself' advent calendar. I'd check out Topshop, New Look and H&M's accessories, grab packs of bracelets, rings and earrings, spilt up the packs to make them go further over the 25 days. Maybe have a nice necklace (or engagement ring!) for the final day.
I treated myself to an advent candle, this one was £3.95 from Flutterbyes. I like having an advent candle because it feels like you can see Christmas getting closer.