You will need two T10 LED bulbs and one 42mm festoon led bulb for the interiour. The boot Bulb is a T10 also incase you want to swap that aswell. Ebay is the cheapest, my advice would be to search and refine lowest to highest price and make sure the location is in the uk. They should arrive quite quickly.
the size of the festoon does not really matter much a 38mm can fit you would just need to bend the terminals at each side.
You do not need them to be error free as they are not recognised by the Canbus system.