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

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

From your image I am not sure what you are looking for. If it is this then I will detail the steps otherwise could you post a better image

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