I suppose any answer will depend on why you want another cat. But all answers should consider the personalities and needs of the existing residents (human and feline/animal) so that the best type of family relationships can form.
I don't think another cat, matched to your present cat, and to your needs, and properly introduced, should impact negatively on your present relationship with your cat. Love can expand!
Matching is crucial. I don't know what your existing cat is like, how much time you have etc, but the little I know about a sphinx cat is that they need a lot of attention and are very active. I am about to get a friend for my cat, and I did heaps and heaps of research and discussion with others - everything in our decision is geared toward the best possible friendship outcome for our resident cat. Here's some useful reading on understanding cat types and compatibilities: