I am traveling to london 4th July I to heathrow at 8am. Going to hotel at Trafalgar Square then sightseeing. Will be doing bus tour either Friday or Saturday then returning to heathrow Sunday afternoon. Was looking at travel cards but done know if we would be better with oyster can I get an Oyster card at heathrow. The travel card for the Friday seems expensive £17 peak as I think we would maybe only do journey from airport and walk about central london near our hotel that day and sat too.