What are substitutions for coconut in curry?
Thai curry recipes often use a lot, and the flavour is distinctive. You'll need to experiment. Your idea of cashews is a good place to start. What I've often used in Indian curries is ground almonds (almond flour would be better but I can't get it easily). They have some thickening power and quite a suitable taste. You could also try cooking with nut milk - I've only done this a couple of times because it's not something I normally have, but recently used some almond milk in a sauce with lentils etc. It ended up with a fairly creamy texture. This was a brand marketed for cooking and a little thicker than I've come across before

As an aside, I hope you've had medical confirmation of the allergy - it's not exactly unknown for these things to be deceptive.