in reality just about every single box spring today is completely solid and non compliance just like a platform bed. just keep in mind that some open space between slats is sometimes desirable to improve airflow.
anyway, here are a list of mattress manufacturers that actually make FUNCTIONAL box springs (more so than just open slat type base which would be used by most reputable latex sellers) and will feel different without a base.
Greensleep Hypnos Hastens Vi-Spring Royal-Pedic
and other possibles would be Duxiana, McRoskey's.
other than these companies I can pretty much guarantee any mattress will be fine for the platform bed so long as it does not go over the weight limit of the platform, you will however likely lose all or part of your manufacturers warranty....although you may find that this may not matter anyway, just thought I would mention it though.