Was looking through their website - they sell (or sold, it seems out of stock) a clear plastic card-sized insert for holding coins. As long as you don't need them often, it would probably be sufficient. But I haven't used it.
I keep my wallet in my crossbody sling bag front pocket. I keep change below it. Though generally I use cards for most things so I don't get much change.
I'd also point out that I had wanted one with the closure flap but I'm glad I got the one without from my partner because it would have caught and popped it open any time I took it in and out of my pocket.
Ok, I see you're an Assassin's Creed character, because the first line sounds a gartment description more complicated than anything I've ever worn. I do appreciate the effort and description though :)
No problem. I have an older model of this sling that has a much smaller pocket back from the days when an iPhone 3 barely fit in it. Now the newer one could fit a modern day iPhone in it, while mine just fits my secrid wallet and change just fine.