No you don’t. As I mentioned in a previous thread (can’t be bothered looking, but I remember pulykammel was involved) there’s plenty of examples of typeset documents with double or one-and-a-half spacing after a full stop. From what I can gather, the “hard and fast rule” that everybody talks about when referencing double spacing is anything but, and a relatively recent innovation. Witness Wikipedia’s take on Sentence Spacing, for instance:
Besides, I’ll say again, virtually every typeset mathematics, physics and computer science textbook uses English spacing, or a near approximation of it. There are still plenty of typeset books being produced today that eschew single spacing, in favour of enlarged spaces after full stops.