The best thing is to use a smart typesetter (i.e. TeX) that'll do the right thing (one-and-half spaces; or French spacing; or presumably whatever else you speci

The best thing is to use a smart typesetter (i.e. TeX) that'll do the right thing (one-and-half spaces; or French spacing; or presumably whatever else you specify) however many spaces you have between sentences. (Two spaces after a sentence [in TeX source] has the advantage of distinguishing between sentences and other places where a full stop might appear, such as in abbreviations.)