The light switch in my downstairs toilet is just a normal rocker type.
ISTM this is somewhat dangerous due to the proximity of basin & WC, so
I'm looking for a safer solution.

Absolutely no need. It is perfectly acceptable to use a standard light
switch in this situation. If you insist on using a waterproof type (i.e. it
is an outside toilet with an ill-fitting door) then consider something like
Screwfix item 16450.

http://www.screwfix.com/app/sfd/cat/...83903&id=16450

I really wouldn't bother, though.

Christian.