Hi Delta2,
I live in Calgary, and I thought it was cold here! I’m amazed you can sleep hot in the great white north! 
I’m very familiar with The Mattress and Sleep Company (tmasc) having bought my own beds there… They are a wonderful company to work with (which is all I can really say since I know nothing about the mattress you’re considering). You’re best off to call them, or sometimes Daniel from tmasc comments in the forums here too so he might comment here.
I often try to help Phoenix out, and make the ‘standard’ first recommendations for new posters, which is to recommend you read the post on host to find the best mattress for yourself. I appreciate some sections might not apply to you, with limited retail supply, narrow budget, and shipping logistics- but at least it might give you some basic principals.
Good luck and feel free to ask any questions.