Hi HappyHunter,
Sorry to hear of your backaches and shoulder discomfort on your old mattress. The firmness level on a mattress topper is a matter of personal preference, depending on your stats(height, BMI, sleeping position(s) and any underlying health conditions) and your PPP(Posture and alignment, Pressure relief, and Personal preferences).
As you are a side sleeper with backaches and shoulder pain, this could be caused by the latex being not firm enough, or, as you say, too firm. As with a mattress, the comfort level of any topper would be specific and unique to you. since you have not given your stats, any suggestion would be guessingā¦the best option would be to try a latex topper in person to see how each firmness level feels, though you would likely need a ābreak inā period to see if it relieves your pain. You can also reach out to any of the Trusted Members of the site, many of who carry latex toppers; if you can provide them a little information and what you are looking to achieve they can match you with a suitable latex topper
You can read a recent Phoenix discussion on toppers inpost #2 here and also this post with a consumer with back pain discussing toppers with member Latex Mattress Factory which may be a good starting point for you, as they are very experienced in matching consumers with quality latex offerings.
Hope this helps,
Basilio