Hi all! I am travelling to London for business and will be staying for a month or more. My place of work is housed in Canary Wharf and I am booked to stay at one of your suite-stays in Stratford. Since I would be travelling to and fro for work- I would need a travel card for using the tube. I had read of the Oyster card. Please advise on where can I pre-order an Oyster Card and where all can I top it up when running low on card balance?