You certainly don't need a check valve on the dhw. The air gap in the dhw header gives more than adequate protection to the cold main for this additionally the flow rate at the tap will be signinficantly reduced by the resistance of the check valve.
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local