Well, a walking commute like that is probably not going to happen in Boston without tradeoffs. I think extremely few people are lucky enough to have a commute like that in the US. That said, Cambridge has a the highest percentage of "pedestrian" commuters in the country.

Anyway, off the top of my head: Medford, Quincy, Braintree. Schools might not knock it out of the park like Lexington but they're not crap either. A decent MA school is better than a lot of "good" schools in other states. However, a "tiny" house is in the eye of the beholder. I'd consider 1500sqft pretty decent whereas some people would want 2000+ with an attached garage, which is incongruent with urban living. The "real T" access alleviates a lot of commute woes; T delays are blown out of proportion compared to the daily car-crash-induced traffic jam.