Without modifying too much the current controls, i personaly would use: Arrows, Z for jump, X to interact and anything in A, S, D & C for the potion. like the RPG maker style, i think they feel more confortable when they are side by side.
Another aproach could be: WASD movement, Space - jump, J & K for interaction and potion.
This would be my pick since not everyone has arows in their keyboards(My case, i have to remap the keys in my keyboard software to play games that need arrows.).
My english is not native, I hope the text is understandable.