Hi Candi,
Unfortunately it’s not possible to make specific suggestions or recommendations with any certainly because you are the only one that can feel what you feel on a mattress or a mattress/topper combination and there are too many unknowns, variables, and personal preferences involved for anyone to be able to predict or make a specific suggestion about which topper would be the best “match” for both you in combination with the mattress you are using it on in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) based on specs (either yours or a mattress) or “theory at a distance” that can possibly be more accurate than your own personal testing or sleeping experience (see mattress firmness/comfort levels in post #2 here).
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 will always be 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. A good exchange/return policy can also reduce the risk of an online topper purchase so I would make sure you are comfortable with the options you have available after a purchase 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.
It would be surprising to me if none of the manufacturers on the Montreal list carried toppers but if for some reason none of them do then it would still be a good idea to test some of their latex mattresses that have softer comfort layers so you can get some sense of the firmness that may be best for you.
Some of the better suppliers I’m aware of that ship mattresses and/or toppers across Canada are also listed in post #21 here.
Any type or blend of latex (either Dunlop or Talalay and made with natural rubber, synthetic rubber, or a blend of both) would be a high quality and durable material relative to other types of foam. The choice between different types and blends of latex is a preference and budget choice more than a “better/worse” choice. There is more about the different types and blends of latex in post #6 here and there is also more about some of the general differences between Dunlop and Talalay in post #7 here but again the most reliable way to know which type of topper or which type of latex you tend to prefer will be based on your own careful testing or personal sleeping experience.
Most people with fibromyalgia are very sensitive to pressure points and will often prefer a topper that is softer than others in the same weight range would normally choose so a 2" or 3" topper that was 19 ILD would be a reasonable “guess” but of course it would only be a guess because you are the only one that can confirm how well you sleep on any mattress/topper combination.
Phoenix