The grammar checker can help enforce 2 spaces. I don't care for it, but go to Word, preferences, Spelling and Grammar, check grammar (as you type/with spelling). Go to settings for grammar; on the REQUIRE change space between sentences from DON'T CHECK to 2 spaces.

Unfortunately, turning grammar checker slows things down a lot. You should probably clear a lot of what the grammar checker will stop/flag. Maybe all of the other settings??