Best mattress style for side sleeping?

Hi,
I'm a side sleeper, the past few mattresses I've owned have been very uncomfortable and left me waking up aching. I currently have one of those rolled "7 zone" mattress on my bed, I feel like it just sinks down and is very hard and uncomfortable. I have to sleep with a pillow between my knees to alleviate hip pain.
I've read so many different reviews and seen these fad mattresses "eve, Simba etc" also one source says a medium firm mattress would be best, others a soft/medium?
It's just me, I tend to sleep more on one side than directly in the middle.
I have a king sized slatted base. I'm 5'8.
Looking forward to your suggestions?