Hi nycgal,
Lower back pain can often be a sign that the mattress is too soft and neck pain is most often a sign of a pillow issue (you will often need a new pillow with a new mattress if your shoulders are sinking in more or less than your previous mattress and your head and neck aren’t in the same alignment).
There is more about the most common symptoms that people may experience on a mattress and the most likely reasons behind them in post #2 here.
There is also more information about pillows in the pillow topic here.
Giving your experience and any “symptoms” you are experiencing a chance to stabilize and making any exchanges based on your experiences or “symptoms” over a little longer period of time rather than based on your initial impressions will give you a much better chance of making the most suitable choice and deciding whether your experience is “pointing to” an exchange for either one or two more firmness increments (to 24 or 28 ILD).
While there are probably more people that are new to sleeping on latex that are a little surprised that it feels firmer than they thought it would … each person is unique and there are also others that like you experience it as being softer than they expected and all of this is a normal part of the process of “fine tuning” an online component latex mattress using your actual sleeping experience as a reference point to help you choose your “ideal” firmness level.
Phoenix