I cheated and bought a slingyroo bag - I love it. And not just because it's made from Northern Lights so it matches my wrap - it also fits a surprising amount of crap and is really comfy to wear. The strap is long enough to go across my body under Alex's butt and can be adjusted to the length I want via the sling rings on the end.
I really want a bag made from a wrap too. I have a lenny lamb here, well scraps of one, to turn into a bag but I still want a ’proper’ one lol

Sent from my Galaxy S3 so please excuse errors.