Hi Sleepwoodbenice,
Welcome to the Mattress Forum! 
There’s more complete information about common questions and appropriate products for growing children in this post and the posts it links to. In general, something that is in the more “medium to medium firm” category is generally recommended.
All of the products you are considering use good quality and durable materials. Latex is a good quality material and a popular choice for a durable children’s mattress.
As for the organic certifications, most people that are looking for an “organic” mattress or materials are usually concerned more with “safety” than whether the materials have an actual organic certification and they usually aren’t aware that an organic certification isn’t the same thing as a safety certification. There is more information about the three different levels of organic certifications in post #2 here and some of the benefits of an organic certification in post #3 here and there is more about the different types of organic and safety certifications such as Oeko-tex, Eco-Institut, Greenguard Gold, C2C, and CertiPUR-US in post #2 here and more about some of the differences between organic and safety certifications in post #2 here and there are also some comments in post #42 here that can help you decide whether an organic certification is important to you for environmental, social, or personal reasons or whether a “safety” certification is enough.
Regarding recommendations, both Memory Foam Comfort and TMASC are members of this site which means that I think very highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. They are extremely knowledgeable about latex and different configurations, and I would not hesitate to recommend them for your consideration, and they also offer discounts for Mattress Underground members. There certainly are other offerings across Canada for all-latex products, but I wouldn’t have such a list, as attempting to maintain a complete listing of the retailers discussed here on the forum and their inventory in a constantly changing market would be a task that is beyond the scope of this forum.
Phoenix