How do I get more buy wishes/whims?

Pick a snob trait

Snob is also a materialistic, you can farm lifetime happiness with a snob Sims, basically they always want to buy stuff and get potent moodlet from new object

I think the autonomy off might be a part of the problem. My sims keep throwing all sorts of wishes but I have their autonomy on full. They just roll wish after wish constantly. I sometimes get rid of unfulfilled promised wishes because something more interesting pops up before I can fulfil the wish I promised earlier. If my sim needs money I tell them to pick a flower (for example) that is then followed by a wish to pick 5 flowers which is followed by a wish to pick 10 flowers followed by a wish to pick 20 flowers. Selling all those flowers is quite lucrative. But if you can't tell them to pick that first flower, best was I can think of that might trigger that wish would to be in a place where there are lots of wildflowers growing. But you might need to have autonomy on to make them wish to pick flowers.