Distinguishing poststructuralism and postmodernism is very difficult, and it was perhaps too hasty of me to be so swift to do so. Really what I was trying to emphasise was the doubled aspect of the postmodern as both theory and periodisation. Poststructuralism, I would argue, has much more to do with the former than it does the latter. I think you are right to identify Derrida here, because deconstruction might be described as the paradigmatic example of postmodern thinking, but it can be easier to begin by understanding it in a poststructural context - that is, as part of the philosophical movement that developed in response to structuralism (Structure, Sign & Play would be the paradigmatic text, in that case).
Another approach is to see postmodernism as a much broader movement than poststructuralism, with a more disparate set of origins. The earliest “postmodernists” were actually to be found in the artistic disciplines rather than in academia and in a sense the theoretical aspect of postmodernism developed in response to the innovations made in the arts. So, you might want to look at figures like Robbe-Grillet, Stockhausen, Rauschenberg, Godard and Robert Venturi, to mention only the most obvious. This merely expands the analysis of that “responsive” or “reactive” aspect of postmodernism.
Ultimately, I think the essential thing to consider is whether the analysis of postmodernity or postmodern theory is explicit or not. The thing about most poststructuralism is that it is not concerned with that idea. Derrida, Foucault, Deleuze, etc. rarely, if ever, talk about the postmodern - indeed, their references are almost universally modern, albeit often in a critical sense. There is no doubt they provide inspiration to postmodern trends and sometimes discuss issues and ideas of great relevance to postmodernity, but it is important to follow the lineage rather than assume the connection. Moreover, to properly understand the postmodern I think you need to deal with both of its key features, and that means engaging with the overt postmodernists rather than the more indirect poststructuralists.
At the risk of waffling any further I’ll leave it at that for now. Perhaps if you have gone away and read a few things and/or have some more specific queries then we can take up the discussion again from there, otherwise I might just be muddying the waters for you!
My Masters thesis, by the way, was on the impact of postmodernist ideas on historical studies and was not published, no, as it was really only a short dissertation with only limited research. In principle I’d be happy to share it with you, but I am not too sure on the rules about intellectual copyright in relation to it, so I’d need to check.