How long are you planning on doing it?
Could you do a theme a month, or each week has a theme in a month? So week 1 - something fragrant - candles, small travel size perfumes, flowers, essential oils. Week 2 - something to read (or related) book, magazine, bookmarks, that little thumb thing to hold the book. Week 3 - something to do in or out, colouring book, national trust cafe cake, possibly even an entry fee (likely for some hidden place, or a really short thing). Week 4 - personal care - hand cream, soaps, face mask, body sprays and for the months with 5 weeks, lucky dip - stationery, hand warmers, coffee, anything.
Might help work out what you want each week if you have to think in a category, and you won't buy candles 3 weeks in a row and then struggle to think what you want.