Hi Beteast,
Welcome to the Mattress Forum! 
I’m not sure where you read this but I would keep in mind that there is no specific type or category of mattress or any specific material that is “better for aches and pains” in general because each person’s individual needs and preferences in terms of “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and Personal preferences) is unique to them. There is only a mattress or a mattress/topper combination that is “best for your aches and pains” (regardless of whether the same combination would be suitable for anyone else).
All the different types or categories of mattresses or materials have hundreds of different options, combinations, and designs and some of them that work well for some people may be completely unsuitable for someone else to sleep on even if they have a similar body type and sleeping style or have similar “symptoms” or health conditions. In other words the design of a sleeping system and whether that specific design and combination of materials and components is a good match for you in terms of PPP (regardless of whether it would be suitable for anyone else) is always more important than the specific type of materials and components inside the mattress.
If the only issue with a mattress is that it is too firm and there are no soft spots or sagging in the mattress then a good quality topper can certainly be an effective way to add some additional softness, “comfort” and pressure relief to your sleeping system but the only way to know whether a specific mattress/topper combination is a good “match” for you in terms of PPP is based on your own careful testing or personal experience on the combination. If you can’t test the combination in person then there is always some risk and uncertainty involved in adding a topper because the specifics of the mattress itself along with your own body type, sleeping position, and preferences can affect which specific topper would be a suitable choice on any specific mattress.
There is more information about choosing a topper in post #2 here and the topper guidelines it links to which along with a conversation with a reliable and knowledgeable supplier (that can provide you with good information about how their toppers compare to each other or to other toppers they are familiar with that are available on the market) can help you use your sleeping experience as a reference point and guideline to help you choose the type, thickness, and firmness for a topper that has the least possible risk and the best chance for success. It also includes a link to a list of some of the better online sources for toppers I’m aware of and a link to the online suppliers that have good exchange/return policies as well (just in case the topper you choose doesn’t turn out as well as you hoped for).
If a mattress/topper combination turns out to be a good “match” for you in terms of "comfort and PPP then it also has the advantage of being able to replace just the topper without replacing the entire mattress if it softens or breaks down before the upper foam layers in the mattress (which is very likely because the upper layers of a sleeping system tend to soften or break down before the deeper layers) or if your needs or preferences change over time and a topper can also help extend the useful life of the mattress underneath it as well.
There are also some suggestions in post #2 here that may be helpful if your mattress is too firm as well.
The OMF mattresses in their showrooms are generally on a box spring as well that provides some additional flex under the mattress (vs a foundation that has little to no flex) so if you tested the mattress on their box spring but are using the mattress on a rigid foundation that has no flex then that can certainly have an effect on the feel and performance of your mattress as well.
Phoenix