Best mattress for lower back pain, due to a herniated disc?

I've been diagnosed with Low Back Pain and have a herniated disc for which I will soo undergo an operation for. My question is, given my condition, which type of mattress should I be using and what would John Ryan advise? I am 180cm tall, weigh between 86-90kg, use an Orthoptedic mattress (although its a bit old, over 7 years) and prefer to sleep on my side. Also, how long does it take to recieve a mattress?