E-Mail Marketing Testing Trauma

Hey guys and girls, how are you?

I have quite the challenge on my hands here, so I will try to summarize it to make it easy to understand:

- I use Getresponse as my e-mail autoresponder, have written 53 e-mails so far and I want to test how each individual e-mail does (in the CTR and sales conversion departments)

- I write all my e-mails in plain text, simply because I sell to consumers and not to (potential) business owners and businesses so assuming they all have computers that support fancy HTML e-mails is a BAD assumption and could mean a loss of sales

- The challenge: GR (and others) allow one of THEIR links to track results with, meaning mysite.com would turn it weirdsoundinglink.com OR obvioustrackinglink.com

- GR doesn't allow domain masking after their "super" update and my shopping cart (1shoppingcart) doesn't support domain masking, however their regular tracking URL COULD be used in an HTML e-mail...

So now my question is: how the heck am I supposed to test individual e-mails when there seems to be no way of using "good looking" (mysite.com) tracking urls?

Does this mean that I will need to switch to HTML e-mails, while that could be bad for business?

Or does it mean that I'll have to test "manually": see what happens when I use shorter intervals, see what happens when I send broadcasts twice, or an entire series of broadcasts, etc.

Could really use some help here because I find the "techie" side of business to be very challenging (and sometimes confusing).