Trudie, this painting has a special place and meaning in your life. I personally would not change it at all.
What I suggest is that you paint another one like it but with another special meaning. I am sure your son, if he were able to see it, would like you to paint it in a way that he can see that you still miss him, but with fond bright memories.

this one with the sunshine that he placed in your heart.

and then hang them in a special place side by side.
By the way, I simply love the symbolism you added into the painting.