I need help me writing a sales letter to my clients.

I place supply teachers into schools and my business has previously focused on day to day supply and long term bookings. However I have now moved into Permanent recruitment and have gained a lot of traction. I would like to write a letter to all of my school contacts explaining I now offer this service which is very different to normal supply .

I have drafted the sort of thing I want to say. I just require some help making it better!!