How do I smooth out two objects (with low poly) that have been unioned in blender 2.8? I'm creating a character for a new game I'm developing and the character is supposed to be very round with plump arms and legs. When i tried to boolean union the round head with the round body it became jagged. I think it's because of the vertices and their connections but I even if I'm right I don't know what to do about it. Any suggestions and is it something that can be solved by sculpting, modeling, or both?

The goal is to have the character rigged and animated so just having a temporary visual modifier isn't what I'm going for. I just want the head to rest on the body but still be able to move it around when I rig it.

I also need to add arms and legs to the main body mesh too.

I put the blender file here in case anyone wants to take a look.
You can join two spheres this way and adjust for your character as the process should be the same.

Create a sphere with 16 segments and 8 rings



Create a second sphere half the size



With the smaller sphere selected go into edit mode and line up the edge loop with the larger sphere. You can do this by eye



Add a boolean union to the large sphere and select the small sphere to join



Apply the boolean and shade smooth with a subdivision surface x2



To transform the body I would add a lattice with a vertex group on the base mesh to limit the lattice influence and this way you keep the head round



you can then transform the body shape as required