Without knowing the specific curry you’re looking to replicate makes it hard to make specific recommendations but a few things have helped me up my game.
The first is what you use to add a sour note. In the west we often use lime juice, which is great to add sprinkled at the end, but you need to get some tamarind paste for the depth of flavour. It also adds sweetness, but you can instead use some sugar, preferably brown or palm.
Fish sauce is a must to round out the depth of umami and I find soy really doesn’t work for me. If that’s a no-go because of dietary restrictions you might have to add some yeast flakes with the soy sauce, but it’s not going to have the same depth.
If you can get galangal, use it. Same with lemon grass. But again all depends on the specific curry.