I purchased a Beautyrest Black Hybrid - King Mattress about a year ago and specified this would placed on a slatted platform. About 6 months into having the mattress, it began to develop a lump in the center. I went to the Mattress Firm to inquire about returning and/or replacing. I was given an inspection/return policy and instructions. It is an extremely difficult process and you can only qualify for store credit or a replacement of the same mattress. Turns out this mattress is not suited for slatted platform beds, but the sales person never told us this. Later I found it the slats can only be 2.5" - 3.0" apart. I have a very high-end bed frame and the slats are 3.5" - 4.0" apart. Therefore, no refund, no return, no replacement! Warning to all buyers with slatted platform beds - do your research & ask questions before you commit to a purchase!
PS - I just bought a new mattress from Tuft & Needle for a fraction of the price and it is AMAZING. I highly recommend for slatted platform beds.