I've had this plant for some 12-15 years, although I must admit it thrived on neglect rather than care for a number of years.
A number of Mammillaria species will hybridise, but I suspect that they will not do it freely, i.e., among any two species. In other words, it depends on the neighbours at the time of flowering. Do you keep similar or close species, maybe other sub-species or possibly other populations of M. bocasana?
As for breeding true, in case it self-pollinates, it will be the same species, even the same population, but it won't be a "clone" of the parent plant - it never is, when sexual reproduction is involved.
Next year, isolate the plant while it is in flower - say, a [different?] windowsill away from the "general" population - and tickle its stamens and stylus with a soft paintbrush. Just make sure you isolate it before the flowers open and keep it away until all the flowers have faded. The seed thus produced will yield true-to-type M. bocasa subsp. eschauzieri.