obviously easiest for someone with loads of luggage is a taxi - but expect it to cost �45-�50, with an indeterminate journey time due to the uncertainties of the traffic - but it can be done in around an hour.
a single tube fare is �4-00, and the journey can be achieved with 1 change at Piccadilly Circus, but carrying mountains of luggage on escalators is not for the faint-hearted.
Express bus 412/500 will take you to Victoria where you can get a 211 bus to Waterloo, bus fare �1-50, coach fare �10-00
actually, there are so many permutations, probably easiest to go to
http://journeyplanner.tfl.gov.uk/user/XSLT_TRI P_REQUEST2 and play around with the travel mode selection to get what you want.......