Hi Jonathan, and welcome to the Forum. The hook spined Mammillarias are often quite difficult to identify without any flowers to help. Without flowers one has to look at body shape, size, spines and whether there is woll or bristles in the axils. Unfortunately these are all variable aspects!
However, your plants is, I believe, is sheldonii. My reasoning is:
M. fraileana has 3 or 4 central spines, one of which is hooked, and I can only see one central spine on your plant. These spines are also usually dark brown, whereas your plant's spines are much lighter in colour. When it flowers you can be pretty sure, because M. fraileana has pale pink/white flowers with a darker stripe. and a long pink stigma.
I am also sure that it is not M. blossfeldiana, which also has more central spines, more radial spines and is a much smaller plant altogether, not ofsetting so much. Its flowers are very distinctive, being very striped with white and pink.
M. sheldonii is a variable plant, and it can have as few as 1 central spine or up to 4, one hooked. It has radial spines from 9 to 24, and are pale. tipped with brown, although I have seen in habitat plant sthat have almost white spines and some with spines almost as dark as M. mazatlanensis. When it flowers, it should have pink flowers, but with a greenish-yellow stigma.
Having mentioned M. mazatlanensis, it is an outside possibility that your plant might be this, as it also is a variable plant and replaces M. sheldonii as you go down the Gulf og Cortez coast from Sonoroa into Sinaloa. However the flowers are different yet again, being larger and a much darker and uniform pink to purple colour, with stigmas that are the same colour.
But I would bet on it being M. sheldonii.