The perfect way of finding the Kingsdown mattresses is online. Try the manufacturers website and get the basic information from there.
After that try the second option which is the online shops like the Amazon or the other resellers.
Make sure to read a lot of mattress reviews as that will only help you find out the best type from the Kingsdown brand.
Once you have found out the reviews then visit the local dealer to try the mattress from your self. Most dealers and shops will agree for you to lie down on the mattress and test it for yourself.
Always check online and offline as to what are the shipping and handling charges.