Just to clarify, you pay the exact same price through MyPost Business as you do over the counter. The price is calculated by using the AP calculator, which is exactly what you want to do.

If you're happy to pay full price for your postage over the counter, then you're really not worried about whether or not you get a postage discount - but if you send just one parcel per week you'll find yourself on band 1 and get a discount anyway. You can still pay for your postage over the counter if you wish (which you say you are doing now), and it will count towards your total spend. To track your spending, all you have to do is get your QR code scanned.

Opening a MyPost Business account is totally free, and scanning your QR code is practically effortless. I mean, you're there at the counter lodging your parcel anyway, so it's not like you're going out of your way, and the process is akin to scanning your Flybuys or Everyday Rewards card.