Hi Grace,
 
Thanks for your question.
 
I am presuming that you are referring to a split tension mattress where one side has say a medium support and the other side has a firm support or are you referring to a zip & link mattress which is when two separate mattresses are zipped together.

 

 
Whether you are referring to a one piece mattress or a zip & link mattress, either can be placed on to a kingsize base.  However as zip & link mattresses do tend to be slightly wider than a standard one piece mattress, you would need to ensure that the dimensions are correct.  If you have a bed frame which has a lip where the mattresses sit on to, then you would need to check the internal dimensions to ensure that a zip & link mattress would fit.
 
If you require any further information, please do not hesitate to telephone the office on 0161 437 4419 and speak to one of our friendly team who will be more than happy to assist you.
 
Kind regards
Julie