Personally If i were you I would buy a Mild curry powder and add a dessert spoon of curry powder.
Adding more won't make it hotter but will increase the depth of flavour.
To add depth of flavour but no heat add a tsp of cumin at the onion frying stage.
Always add the powder at the end of the onion frying stage (be VERY careful not to burn) and then add liquid.
Curry powder goes off after only two months, so if you find the curry bland it could be that!