Also, I think there is no great taboo against using 奥さん to refer to your own wife. I think kanai might be more humble, probably because the "san" part of okusan means you are using an honorific on someone in your "in group", which is generally avoided. But in the case of okusan it is an essential part of the word, so you can't leave it off - hence some people might hesitate to use it. I think okusan would actually be preferable to tsuma when talking among friends or close colleagues. Toritoribe-san will (hopefully) correct me if this is wrong.