Dear Mr (NAME)
Re Conservatory at above address
We are writing to express our utmost delight with the conservatory which was recently completed by your company.
As you know we were disappointed not to have had it in time for Christmas but at the time we last spoke you suggested that it would be "worth waiting for". Well we have to admit that it certainly WAS worth waiting for.
We were very impressed with the clean and efficient way in which your representatives operated during the contract and also with their very pleasant dispositions. Will you please pass on our sincere thanks to them also.
In conclusion we would like to mention that we would have no hesitation in recommending your company whenever the opportunity presents itself.