Helen Deborah Vecht wrote:

Download next year's Fares leaflet from the TfL website, get confused &
exasperated, then make up your mind...

http://www.tfl.gov.uk/tfl/fares-tick...007.pdf#page=1

Thank you. Getting the absolute most economical solution probably isn't
essential for a once/twice a year trip. I wasn't aware that you could load a
"travel card" on an Oyster card, so that with a little extra PAYG deposit should
suit my needs quite well.