The letter combinations/pairing of: o_e, oa, ow, oe can also make the long "o" sound. Here is an interesting "o" word for you, did you know the name for "pound" key (#) it's "octothrope". I guess hashtags weren't a thing when they dreamt up that word. Another cool fact, the word "dreamt" is the only English word to end with the letters "mt".
The most common long "o" words are: go, so, no, bone, joke, rose, close, boat and soap. The most common short "o" words are: cop, dog, hot, jog, mom, mop, pot, son and won.