Hi radorix,
There are a wide range of innerspring mattresses that may have softer or firmer support cores and softer or firmer comfort layers and some of them may be a good “match” for you in terms of PPP and some of them may be completely unsuitable for you to sleep on and lead to back pain.
The same would be true for two sided mattresses which are also available with softer or firmer support cores and softer or firmer comfort layers. While a two sided mattress is generally more durable than a one sided mattress that uses the same materials and components (see posts #2 and #3 here) … it certainly is no assurance that a mattress will be a suitable “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) or that it will help with back pain.
There is more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel” and how the different layers in a mattress can contribute to good alignment.
I hope your current mattress works out well for you but if it doesn’t and you need to find something different again then the testing guidelines for alignment in the tutorial post may be helpful. In general terms I would make sure that the support layers of the mattress are a suitable firmness for your body type and sleeping positions and that the comfort layers are “just enough” in terms of softness and thickness to relieve any pressure issues you may have in your most pressure prone position and no more because with thicker/softer comfort layers (or softer support layers) you can increase the risk of sleeping out of alignment and the back pain that can go with it.
Assuming that your back pain is a mattress issue and not a back issue (if it’s a mattress issue your back pain will tend to go away soon after you get up and more around and stretch a bit) … dealing with a knowledgeable and experienced manufacturer that has the experience to be able to help you identify any patterns in your choices that may be contributing to back pain can be one of the most important factors in making a successful mattress choice.
Phoenix