Hi JL9977.
Welcome to our Mattress Forum. 
Sorry to hear you’re not having success softening up your sleeping experience on your Dormeo bed. Without knowing the specifications of that bed, any foam ILD/IFDs, etc. it’s hard to say why you may be experiencing back pain but this forum topic could be useful to you in identifying what may be the root cause.
While hearing others opinions can be useful, we always caution people to stay away from reviews when looking to purchase a mattress. People often review mattresses far too early after receiving them, and reviews lack specific information about all the variables that can contribute to the suitability of a mattress (like details about the person and the mattress) that would make them more meaningful/accurate. We also suggest reading about the dangers of making a purchase based on reviews here.
You also mentioned your sleeping positions - this is super useful in identifying your ideal comfort layer. We have a resource that speaks to the needs of different sleeping positions here.
While I’m sorry that I cannot make a specific recommendation, I hope some of the above resources help you to narrow your choices and make a decision that best fits your needs.
NikkiTMU