24" mattress height is our default. Any other size will raise/lower the entire bed, not just the mattress.
Please let us know at time of order the thickness of the Mattress and Box Spring (if applicable).
The default support is for a box spring below the mattress. If using a mattress with no box spring choose the "direct slats" option. We will build your bed to compensate for the mattress thickness such that the bed height is the same.
There is no clear advantage/disadvantage to using a box spring under the mattress.
Queen beds and larger have a center support with leg running down the middle on all support configurations.