@Keet
Check the list I linked visually for the character you're searching for. And you probably (should) use the single straight quote more often than you think: you're, have at 'em, 'allo 'allo, it's, etc. etc.
Sorry, but we disagree on this one. Check any published novel, and you'll note that they ALL use curly single quotes ("& rsquo;", in fact). That's a publishing standard, even with leading opening single quotes, NONE of them are straight.
Exactly, the curly quotes are always used in pairs, which is not applicable for the quotes used to indicate feet and inches.
I've NEVER seen that stated anywhere. Now, if you're talking about dialogue, it makes sense, but even then, it breaks down completely for multi-paragraph monologues, where the trailing quote is dropped to signify that they'd not finished speaking yet.
I'm not sure which software you're using, but I've never encountered any software that obsessive/controlling as that, and even if they did, I ignore enough wrong-heading spell-check reconditions to ignore that one too.