Hybrid 4 or Fusion 3

Hi, We recently bought an Eve mattress and are currently in the process of sending it back as it is too firm a mattress for my wife and has been giving her backache from day 1. We stumbled upon your website by chance and looking at your reviews on Trustpilot decided to purchase a mattress from you.My wife is 5'7" and 10 stone and i am 5'9" and 13 stone. Please note that we are vegans so choices from your range are limited but we really can't decide which of the Hybrid 4 or the Fusion 3 would be more suitable. We are both side sleepers and my wife also has Fibromyalgia and suffers joint pain.