My usual answer for street photography is a Ricoh GR. But, I think you're actually more interested in how to carry your K-3ii.
My smallest DSLR bag is a Lowepro Format 160. It can barely squeeze in my K-1, 15-30, and 28-105. It's a tight fit because the 15-30 is a big lens, but still offers enough room for spare batteries, lens cloth, etc. Your camera and lenses are smaller so maybe step down a size to the Format 140.
Format 140 | Lowepro
I usually carry it diagonally with the strap on the left side of my neck and the bag on my right-front for walking. To reduce the risk of a pickpocket cutting or unfastening the strap, I also hold the top handle in crowded places. The bag is small enough to sit on my lap when I stop to eat.