Word Usage – Differences Between ‘Killjoy’, ‘Party Pooper’, and ‘Wet Blanket’ in American English

At least in my (American English) usage:

Blanket: a warm bed covering that is much thicker than a bed sheet, but is only a single layer of material. It's usually woven or felted.

Afghan: a blanket that is coarsely crocheted. More associated with warming your lap while sitting than with a bed covering.

Throw: a light blanket meant to be draped (thrown) across a chair or sofa and used by the chair's occupant if necessary.

Bedspread: a colorful, medium-weight bed covering that makes the bed look attractive when fully made up. It may or may not be removed for sleeping.

Comforter: a warm bed covering that has a decorative cover and some sort of filling (down, polyfill, foam, etc.), but is sewn shut. You cannot remove the filling. Often used instead of a bedspread.

Quilt: structurally much like a comforter, but the cover is often made from many pieces of cloth sewn together in a decorative pattern, and then the whole thing is "quilted", which means criss-crossed with stitching. Popular as folk art.

Duvet: A more recent European import, once rare in America but now increasingly common (the comforter is becoming an endangered species as compared to the duvet). A very plain cloth envelope filled with thick fluffy filling like a comforter. Unlike a comforter, there is a separate duvet cover that is decoratively colored and can be removed and washed separately.

Teetotaller is the noun which is used for such a person, i.e., a person who NEVER drinks alcohol.

Sober is an adjective which means not drunk. It doesn't mean never drunk - it says nothing about drinking habits per se, just that whoever is described as sober is not currently drunk, or appears not to be drunk.

You say that teetotaller sounds stilted, but that isn't the perception of native speakers. It's a fairly common informal word, and probably most native English speakers will know it.