I call all of it "sweaters." Cardigan sweater, crewneck sweater, turtleneck sweater, V-neck sweater, etc.
As far as the blog post, you can call it whatever you like as long as you define your terms. You may want to continue using the terms you are most comfortable with, but in each and every post you do something like this:
"It's winter and time to bring out the knitwear (my term for what many of you know as sweaters). Today I wore a lovely jumper (another term for a sweater for you Yanks) with a cardigan on top. Tomorrow I plan to break out my denim pinafore (what you Americans would call a jumper -- wow, this is complicated!) and take it for a spin."
It may seem a little cumbersome but I think you would get used to it and I really think it's the clearest way to deal with it. If you don't like the parentheses, will your blogging software do footnotes? Or maybe do links to a glossary?