[gvurrdon]

I find that sometimes, after the "OK Google, send a text to $PERSON" my watch will ask whether it should be to their mobile, work or home landline. A way to set it to only send text messages to mobiles would make sense but I can't find any way of doing that.

[TeMPOraL]

You probably need to go to Contacts and long-press on the proper number, and use "set as default" (or something similar) option.

[gvurrdon]

I have in fact set it as default, but the watch still likes to ask "which number".