Downriver from Ham ferry, about a mile along the towpath past well-to-do moorings, is the splendid Richmond Bridge. It's the oldest surviving bridge in the whole London stretch of the Thames, built in 1777, and is Grade I listed. (They widened it in the 1930s, but used the existing stonework.)
Cross south over the bridge and enjoy a free-refill weekday coffee at the cafe in the arch, directly under the bridge (turn right and go back on yourself), which will be full of young mums and their children who are all, they will inform you, very bright for their age. Or try Steins, the sociable Bavarian Beer Garden just a bit upriver where you can practise your sausage, Kartoffel and prost skills.