Hi inputchip,
Welcome to the Mattress Forum! … and I’m glad you found us.
The first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for that are involved in each of them and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability, durability, and value.
The choice of materials and components in a mattress is primarily a preference choice and not as much a “better worse” choice (assuming that you are only considering good quality and more durable versions of the materials and components you prefer). If you tend to prefer the “feel” and “bounce” or even the “familiarity” of an innerspring mattress then as you mentioned it may also be worth considering an innerspring/latex hybrid which uses an innerspring as the support core and latex as the comfort layers.
There is more about innerspring/latex hybrids in post #13 here and the posts it links to.
There are a few all latex mattresses that are in your budget range and posts #3 and #4 here include some links to some of the lower budget latex and latex hybrid mattresses I’m aware of.
The Casper mattress doesn’t really qualify as a “latex” or even a “latex hybrid” mattress since it only has 1.5" of latex which isn’t really enough to include it in a latex hybrid category although the latex they use is the top layer in the mattress so it would have a bigger effect on how the mattress “feels” than the memory foam or polyfoam underneath the top layer.
You can also see some comments about the Casper mattress along with some of the other “simplified choice” mattresses that also have a similar return policy in post #3 here.
The most reliable way to assess the durability of a mattress or know whether it has any potential weak links is to make sure that you find out the type and quality of the all the materials inside it (see this article). There is also more detailed information about the many variables that can affect the durability and useful life of a mattress relative to each person in post #4 here that can be a much more reliable indicator about the durability and useful life of a mattress than the name of the manufacturer on a label, mattress reviews, or the length of a warranty.
The better options or possibilities I’m aware of in and around the Edmonton area (subject to the quality/value guidelines I linked) are listed in post #136 here. The Calgary list is in post #2 here.
Post #21 here also includes some of the better online options or possibilities I’m aware of that ship across Canada as well.
Phoenix