@Gemma_lou What year is your car? If it's a FL (Face Lift) you probably already have the correct door modules. Your best bet if fitting yourself would be to keep an eye on eBay or similar and there is also the for sale section on forums. Another thought which will cost more but get them quicker is to use a retrofitter to supply/fit/code which can be done in a day.
Full kit available on eBay
here