Hello - Not in SW11, but next door in SW12 there is a great lady who did an alteration for me the other week.
I noticed she had had recommendations here years ago, but needed a very fussy bridesmaid dress to be taken in and didn't want to do to a Dry Cleaner alterations place so went there and hoped for the best.
She did an amazing job! She is based on Bedford Hill so out of Balham Station and go under the bridge that heads towards Tooting Bec Common, walk a few seconds as she is away from the High Road.
The company is Perfect Alterations, she is a seamstress so knows what she is doing and is based in the basement of a hairdressers, but has an A board outside with her company noted!
Very happy I am going to be wearing a dress that fits me well for my brother's wedding on Saturday
She also cost about half it would have cost if I went up-town, the only downside is that her card machine was out of action, so I had to do something I never do - get cash out!