We've done this recently and used Steel & Shamash at the Waterloo Road end of Baylis Road / Lower Marsh. We saw Andrew Dowie and he was really good, very helpful and offered sound professional advice. No one wants to think about Wills, but he made the whole process far more painless than we were imaging. We'd kept putting it off because we thought it would be a long drawn out, stressful, time-consuming process - it wasn't! We had an initial meeting to discuss what we wanted to do, after which we were sent draft documents to approve, then we went in to sign them and have them witnessed. Hope that helps.
Not local, but highly recommended - particularly because the guy comes to see you. We used an outfit called Charter Wills. Based in Surrey, but that's irrelevant. He knew his stuff and the price was very reasonable - cheaper, I suspect that most solicitors.