Hi issi81,
You are somewhat fortunate because you still have lots of time before you need to make a decision. While I certainly understand that “the sooner the better” so you can get some good sleep … it’s better to take the time you need first to learn how to make the most effective choice so you can sleep better over the next decade or so (hopefully) that you own your mattress instead of making a rushed decision that may feel good in a showroom but won’t feel so good in a few months or years down the road.
Unfortunately that’s true … but most of it would still be very relevant in helping you make the best possible choice. The posts I linked about making a comfort exchange would also be directly relevant and have some very useful information for those that are in your circumstances.
Keep in mind that you are looking at several criteria that are important for any successful mattress purchase (or exchange).
The first is testing carefully and objectively for support/alignment.
The second is testing carefully and objectively for pressure reliev/comfort
The third is making sure you know all the details about the quality of the materials in your mattress … especially the comfort layers … because this is the biggest factor in durability and how long the mattress will last. You can’f “feel” durability in a showroom because low quality and high quality materials can feel the same. If you aren’t able to find out the specifics of what is in your mattress (which is much less likely in a chain store) … then minimizing the use of suspect or questionable materials is the best you can do.
That depends on the underlying cause behind why you aren’t sleeping well and whether they are connected to alignment issues (typically pain or discomfort in your back or joints), pressure points (typically tingling or numbness in the limbs or issues related to pressure on joints), or something else (temperature regulation, motion isolation and many others including health conditions).
A mattress will go through an initial break in period where the foam lose their initial “false loft” or softness, the materials settle, fibers will compress, and the mattress cover will loosen and stretch. This can make a significant difference in how the mattress feels and performs and in general you can expect it to get softer. You will also go through a initial adjustment period with any new sleeping surface as the body loses it’s “sleeping memory” and gets used to the feel and performance of a new mattress. This can happen whether the mattress is better or worse than your old one and there can be some discomfort during the break in and adjustment period. As you go through both of these your mattress or “symptoms” will either tend to get worse or better until they stabilize. If they get worse then of course the mattress isn’t suitable for you because even after the initial break in period it will continue to soften … just as a slower rate (depending on the quality of the materials). If symptoms get better then you are going in the right direction and the initial break in period is working in your favor. In this case it would depend on how it was when it stabilizes. In most cases … this initial adjustment and break in period will take up to 90 days but it is usually under 30 and in some cases can even be less. There are some suggestions in post #2 here that can help during this time as well to eliminate any other potential causes that are contributing to any discomfort.
Post #11 here may also be worth reading to give some insights into body alignment on a mattress which along with pressure relief are the two most important functions of a mattress.
In your case your lower back symptoms tend to indicate firmer support relative to your weight to control pelvic tilt and your joint and pressure issues tend to indicate a comfort layer that is soft and thick enough to relieve pressure without being so soft and thick that your pelvis will sink in too far and tilt before it is “stopped” by the firmer support layers. With pressure relief and comfort … just enough but no more has less risk for alignment.
Phoenix