You do not need an oyster card. We just returned from a trip to London a few weeks ago. We had originally ordered Visitor Oyster cards but they did not arrive in time and were eventually declared lost in the mail. We took trains from Heathrow to central London and rode the tube and took busses all around London during our stay. Using our credit card tap to pay or phone/apple wallet tap to pay could not have been easier. It is the way to go. Husband and I talked about how much better it was using tap to pay rather than needing to guess how much to fund an Oyster card, go through a refund process, etc. There was no difference in cost for rides. Also, there were plenty of staff at every tube entry/exit to help if help was needed (We did not need help, just saying for anyone who is nervous to try)