I would go with Restonic rather than C4. I had a queen size custom made by Restonic it was excellent and their customer service is good too.
In my experience C4 mattresses are something I would run a mile from!
ETA have not tried Everest so cannot comment however all the locally made mattresses I have ever had here with the exception of Restonic have been really awful.
<em>edited by Di@DXB on 24/12/2014</em>
We need to have a mattress custom made and were thinking of trying Everest Furniture Factory in Al Quoz. Does anybody have any experience with their product and service or can recommend a company to make a mattress for us?