A bit late but you might want to have a look at docker multi-stage build documentation which does exactly what you did (start from a base image then copying stuff from it to your own image), something like that:
Which will simplify building new images against newer “build” image newer tags easier.
btw, you were quite creative on this one! You also might want to have a look at the distroless image, the goal being to only have the bare minimum to run your application in the image: your executable and its runtime dependencies.