In ordinary conversation, only one has the same meaning as one and only one. The shorter phrase is used almost every situation. In mathematical logic, it's often desirable to make a distinction between zero or one and exactly one. In that situation one and only one is used to indicate that the count cannot be less than one or more than one.
For Only in the upper class, the only restricts in the inclusion (in, as opposed to out). But no matter which you restrict, there are only two groups under discussion -- upperclass women and and female commoners.
Only does not carry a vague implication of a small number. It carries a connotation of a small number, sometimes one alone; an only child, the only redhead, the one and only. Only: "being the single one or the relatively few of the kind; having no sibling or no sibling of the same sex; single in superiority or distinction; unique; the best."
phrase meaning - Does "one of the only" actually mean anything ...
I'd use the one with the "not only/but/also" construct: Thanks to his remarkable performance on the SAT, not only was he accepted into Harvard, but he was also given a full scholarship. "not only [fact A] but [fact B]". When you start with "not only" you're indicating that two facts A and B will be presented. Fact A is something that is already good enough (or bad enough) by itself and fact B ...
P2. only but (also but only): (a) only, merely; (b) except only. Now poetic. Source: Oxford English Dictionary (login required) Below are some only but examples from the Corpus of Contemporary American English. Swap in only or nothing but for only but to see: Ultimately, there is only but one choice for you, no? To consume the entire pint. TV ...