This is regardless of income I'm curious what you buy that is just for you? It could be something you need / want or something completely indulgent!
I don't set any sort of monthly budget as such and some months I hardly buy a thing but when I do spend I will spend on things like nice stationary, good skincare, perhaps a magazine, a quality candle, tea and cake out, books and sometimes tech, ipad, smart watch etc. I have netflix and an amazon music subscription but I let dp use them.