Hi rl4518,
Hopefully some of the members here that have similar back issues will see your post and share their comments and experiences.
I would keep in mind that most sleeping ergonomics studies clearly indicate that for most people the single most important factor in how well and how deeply you will sleep on a new mattress will usually be how well it keeps your spine and joints in good alignment (see this topic) and that pressure relief is usually secondary to spinal alignment.
Zoning systems can also be useful and well worth considering for people that have more difficulty finding a mattress with the right “balance” between comfort/pressure relief (under the shoulders especially) and support/alignment (under the hips/pelvis especially) or who have more challenging circumstances or sensitivities, body types that are more difficult to “match” to a mattress, more complex medical issues, or who have a history of having more difficulty in finding a mattress that works well for them. There is more about zoning in this article and in post #11 here and the additional posts it links to.
Some of the information in post #3 here may also give you some insights as to whether you would sleep better on a new mattress than the mattress you are currently sleeping on.
Phoenix