Which small bag (16-20l) should I take!?

I'll be travelling to Central and South America for a year and taking the Osprey Atmos 65l which will include camping equipment for thru-hikes etc. I'll also be spending time within cities and doing a bit of day hiking. I was hoping to find a bag (16-20l) which would be comfortable to wear all day around a town or a day hike, but will also fold down well enough that when doing our thru-hiking I don't have to continue to hold it.

I've seen the Gregory Nano 16 but unsure on whether it would fold down well enough? Any suggestions would be appreciated!