how about combining your handpainted diffuse with a normalmap baked from a highpoly following your forms from the diffuse map? you could bring in some exaggerated hard edges, to mach the stylised look.
I was curious myself, how that might work, so I did some testing: (hope its ok I used your texture for that..) the modeling is rathter simple of course baked a normal-map and a height-map put them in engine with normal and a paralax-effect based on the height map. I think that might give a handpainted diffusetexture like…