Hi cevulirn,
In case you haven’t read it already … the first place to start your research is post #1 here which has all the basic information, steps, and guidelines you will find most helpful in finding the best possible choices … and avoiding the worst ones.
The ability and willingness to provide this information is one of the most important parts of a mattress purchase (right alongside of good testing for comfort and support) because without it you can’t make an informed decision or make any meaningful quality or value comparisons with other mattresses. If they don’t know and/or aren’t able or willing to call the factory to find out (for the manufacturers who provide this information to their retailers in the first place) … especially for the foam in the comfort layers that are the weak link of most mattresses … then it’s usually much safer to assume that they are lower density and walk away. I wouldn’t even spend any time testing a mattress if I didn’t know ahead of time that if I liked it this information would be available.
The better options and possibilities I’m aware of in the Atlanta area are listed in post #2 here.
The longest “standard” size would be california king which is 72" wide by 84" long. Local manufacturers can often make custom sizes to any dimensions you choose so that’s always a possibility although it can add to the cost. A cal king is 8" longer than your height which is generally enough for most people (a mattress that is 6" to 8" longer than the tallest person that uses it is the general guideline that is most often suggested) although extra room can certainly come in handy (I’m 6’ 5" and sleep on a queen so I do understand :))
Phoenix