I recently bought (3months ago) a queen size Serta Siesta Elite Pillowtop Mattress set (anyone heard of this mattress model) and have been sleeping on it for a couple of months.  When I first slept in it (first 15 min.) it felt great.  However,  when I wake up in the mornings I get lower back stiffness and pain.  Does anyone know how you are supposed to "fit" in a bed?....i.e, should you be "cradled" on the mattress and how "deep" should the mattress go down on your hips/butt when you are sleeping in it.  I am a side sleeper primarily. 

I am getting the feeling I am not getting the lower back support that I need.  Is there anyway for me to "firm" up a softer bed.  I heard from many that it is not possible, you can only soften a hard bed.  I am past my 60 day comfort gurantee so I cannot return the bed.  I am hoping for a good solution without losing my shirt in purchasing a new bed.