I can't help with your area directly without knowing what street you're on, but you should be able to connect to some of my longer loops without issue (likely via W. Boylston Street). My go-to almost-10 mile loop is, from my house, Newton Square, east down Highland, left onto Park, cut into Institute Park boardwalk via Rumford Ave, cruise down Grove St, stay right onto Humboldt, left onto Salisbury, right back onto Grove and on to Main St for a downtown run, up Elm Street back to Elm Park (you can look around Elm Park for extra distance), down Park Ave, right onto Chandler all the way to Tatnuck Square, right onto Pleasant St, Pleasant back to Newton Square. I will sometimes cut across June St and do Pleasant before Chandler depending on what kind of hill situation I want to deal with (going up Chandler is mostly uphill but fairly gradual; going up Pleasant is extremely steep but gets it over with). Also the hill up Elm St from downtown is a beast but short and satisfying. If you really want some hill pain I suggest adding miles on where the map says June Street--Morningside, Havelock, Colonial, Westview--or between Highland and Park/Institute Park you could do Germain and Farnum up to Bancroft Tower. I will add that only Pleasant St has relatively shitty sidewalks; you could cut back to Chandler along May St (or any other route) if it was particularly bothersome.

Here's the route: https://onthegomap.com/s/fvrulaal

Only major slowdowns are intersections at Highland and Park, Grove and Main, and Elm and Park. For most of the rest of it you shouldn't get too bogged down at intersections if you stay on the inside of the loop.

Bonus is that it's very easy to turn off this route pretty much anywhere to cut into some other neighborhoods and add more mileage. I'd say just about any street inside of this route will have sidewalks or, if not, will have next to no traffic and is safe for road running. I added Richmond and Vassar to that route to show a common loop I'll throw in for an extra mile ish.