Hello Moux,
Matelas Lapensee
is a local manufacturer with locations in Orleans, ON and Gatineau, QC. They have been making mattresses for over 100 years and make a wide range of mattresses including memory foam, latex, and innersprings. They are transparent about their materials they use and would be well worth considering as a good option in the Ottawa area.
Besides Matelas lapensee, there are two other local factory direct manufacturers I know of that have stores close to Ottawa ...
www.matelasdauphin.com/en/home/ A regional factory direct manufacturer with 15 stores in Quebec including Gatineau. They also make a wide range of mattresses including memory foam, latex, and innersprings and are transparent about their materials as well and would also be well worth a visit.
obasan.ca/ Factory direct store for SleepTek in Ottawa. They make some very high quality latex mattresses that can be customized with your choice of layers but are also in a more premium price range.
NOTE: there are three additional options in the next post if you scroll down.
Of course there are many more in the Montreal area but that is quite a drive away. All of these are using higher quality materials and are typically better quality/value than most of the mainstream choices in the area.
If you are looking at memory foam ... I would make certain that it was high quality (5 lbs/sq ft) as lower densities will soften and break down more quickly, especially with higher weights. I would also tend to use the thinnest possible layers that provide you with good pressure relief as memory foam is a non supportive material and if the layers are too thick for your weight distribution or sleeping positions they will contribute to sleeping out of alignment. Memory foam can be long lasting in its higher densities but it will generally not last close to 20 years (10 to 12 would be a more realistic expectation).
Other options that may work well for you is softer latex in the comfort layers which is more durable and supportive than memory foam and any of these could be over a support system of latex, innersprings, or good quality polyfoam. Innersprings and polyfoam will (or should) be lower cost than a latex support system. The comfort layers are the weak link in the durability of a mattress and this is where higher quality materials are the most important.
One final comment is that the support system needs to be firm enough to provide good support to the heavier areas of your body (particularly the hips) so while the comfort layers can be soft to provide good pressure relief and the softer feel you like ... the support layers still need to be firm enough to provide good support.
Phoenix