All the London railway stations :
Coulsdon South is on ThamesLink.
This is a Category A station: This station has step-free access to all platforms via lifts.
Ramps maybe needed to get onto trains
See pictures and further accessible transport in London detail from links below.
National Rail : ThamesLink
AccessAble Access Guide :
Accessibility friendly : Level access to platform 1 (to London). Steps to platform 2 (Redhill).
General description : See wiki
More comment : National Rail Map & Guide.