Do you want a thing, or an experience?
If you want a thing...as mentioned, be mindful if it will also remind you of your ex.
If its an experience - Spa, just getting your hair and nails done with nice lunch, theatre or a family day out.
If its a thing, I'm afraid my mind is sitting in the practical today...so a nice kitchen gadget...it might just the right time to get an ice cream maker or soda stream.
An upgrade on practical item, like knives or pans. Not the most glamorous but they'd give me joy using them for weeks.
Clothes, books.
A subscription....not sure how many months you'd get but flowers, wine, coffee, stationery, all manner of stuff can be delivered monthly and would treat you for longer than a day.