Hi DrButterscotch,
There would be no harm in terms of comfort and support (the floor is a solid non flexing surface which is what a latex mattress does best with) but it would reduce the airflow and ventilation of the mattress and it may also be risky in terms of mold and mildew, soiling and hygiene of the mattress (close to the floor on carpet is dustier) and other unwanted “visitors”. Of course it also wouldn’t be the ideal height above the floor for most people. This first post in this thread has some lower cost options than $300 which may be better (such as some of the grid type foundations which don’t require a metal frame). Generally a foundation that is either slatted or a metal grid is best of all for a latex mattress rather than a solid surface which restricts airflow.
Just in case you haven’t seen this … post #2 here has some of the better options in the Atlanta area that I’m aware of.
Phoenix