[shiomiru]

"ou" is fine too, actually. See the proposal p. 14 (=16 in the PDF): https://www.bunka.go.jp/seisaku/bunkashingikai/sokai/pdf/942...

(To differentiate between the case where it's actually two vowels, you have to put an apostrophe inbetween; their example is 小唄 -> ko'uta.)