Assos bib sizing is more biased towards height than weight, so go for the medium. For reference, I'm a couple of inches taller and narrower, and the mediums are fine.

BTW, since this is apparently your first pair of Assos bibs, when you first put it on, you'll think it's too small. However, once you're on the bike, the famous Assos cut comes into its own and demonstrates why people love Assos bibs so much.