With some tinkering and ward-splitting, it is possible to get much better constituencies in this area, avoid splitting Wimbledon or Mitcham & Morden, and yet still retain coherent Wandsworth constituencies.
Lambeth, which consists of five broad areas (Vauxhall, Clapham, Streatham, Brixton, and Norwood) needs to be dealt with carefully in terms of preserving community identities. Transport links must also be considered as well as historical connections, particularly those between Streatham and Clapham (Streatham has included most of Clapham since 1974); I firmly believe it is time the community of Clapham was reunited, its northern half being separated from Vauxhall. This allows a return of the old Brixton constituency, latterly called Lambeth Central until it was split up in 1983.
As for Croydon, splitting two of its wards can minimise change as much as possible, because the awkward average ward sizes otherwise make drawing sensible constituencies in Croydon impossible without breaking up Carshalton & Wallington, which is also not desirable either. As long as ward splitting is performed carefully, there is no reason why it should be completely ruled out in order to preserve geographical and cultural ties within an area. Sutton's constituencies should expand eastwards, not westwards, to minimise disruption.
My alternative constituencies for South London are:
Streatham & Clapham succeeds Streatham and contains the entirety of both communities.
Battersea & Vauxhall succeeds Battersea.
Balham & Tooting succeeds Tooting and is similar to the 1918-1950 Balham & Tooting constituency. It contains polling district FDC of Furzedown ward, making its actual electorate 72,784 and the changed Mitcham & Morden's actual electorate 73,879.
Croydon East succeeds Croydon Central and apart from losing polling districts HE4 and HE5 of Heathfields ward to a changed Croydon South, has the same boundaries as the current Croydon Central. Its actual electorate is 71,114. The real electorate of Croydon South in this plan is therefore 72,022. Croydon North loses polling districts BG1, BG6 and BG7 of Broad Green ward (this is the only change to this constituency) to a changed Carshalton & Wallington, making its new electorate 76,524 and Carshalton & Wallington's new electorate 75,686.
Brixton is a new seat, although a very similar seat has existed before.
The next section of my alternative boundaries series focuses on North East England.