I think part of the problem is that the straps are not padded especially when you mention that your shoulders are what is hurting the most.

An apron tie is what you should use with any carrier where the waistband is not padded as it is most suportive for baby and distributes the weight better for you.

Basically you take the waistband straps and put them around your waist so that the carrier is hanging down with the front facing your legs like you were putting an apron on...once you have tied them of you lift the carrier up but DO NOT flip the waistband. This forms a kind of sling or hammock section for baby's bottom using the main part of the carrier as the support/seat not the straps as would happen otherwise...does that make more sense?

the waistband straps should sit around your true waist not donw towards the hips like padded carriers do and baby's bottom should be level with your waist when tied correctly...this helps you to know when you have the right tension on the straps when baby's bottom is in the right place.....too low and that also places extra stress on the shoulders to take the weight. HTH...

If you live anywhere near Langwarrin you are welcome to come and try a babyhawk and pikkolo on for size!