I love treating myself to a nice jam or nut spread. Either the supermarket premium brand, or even sometimes Selfridges/F+M/Harrods. Usually £2.50 - £7 a jar, but it'll last me easily a month or two. As well as being good quality, there's usually more variation in flavours than the cheaper stuff. I like to match to the season, so caramelised apple in Autumn, spiced fruits at Christmas, mango/tropical flavours in the summer...
I tend to get a lot of skincare at Christmas, Birthdays etc. I save the good stuff for a treat. Technically free as I didn't pay for it.
Making myself a nice drink. Adding ice, using a "good" glass, adding a squeeze of lemon etc. Just slightly elevated, but very little cost.
On the more expensive side, I'm currently cultivating an elevated wardrobe using good quality brands. Each individual purchase has been chosen carefully to be timeless and adaptable. While definitely not cheap, I can truly say I love every purchase (think White Company, Reformation, Hobbs). Despite the upfront cost, I'm finding this to be quite cost-neutral in the long run.
I used to panic-buy outfits for events - sadly never really being in love with what I bought, but still parting with upwards of £70 per event. I now have at least one outfit that I feel fantastic in for most occasions, ranging from casual to very formal. It's also worth it mentally to not have to do the panic rush to the shops to sweatily try find a dress or skirt. My clothing spend yearly hasn't changed, I just buy fewer, much higher quality pieces.