Ah, but the volume of an object increases as a cube, so if we increase the sphere so that the increase in the radius is 3, that would increase the volume by 27. Since we want to have a surface gravity similar to earth, that would mean the density of the planet to be about 2.04. (mass increases by 10, volume increases by 27, density of the earth is approximately 5.52)

Interestingly, that is very close to the range of the bone density of many animals, so the answer is obvious. We need to find the skeletal remains of a spherical space whale that is 3 times the size of the earth, and immigrate there.

Of course, with my luck, it would already be inhabited and I would be put to work in the calcium mines.