The prayer bead before the monk in the house was the only one I can recall in that area that I would consider really well hidden. I got the water mechanic and found one under the water shortly before that. I did feel pretty special finding that bead though.
I'm one bead away from 17 vitality now. I ended up playing a bit more and went back to ashina castle and collected most of the idols a second time. I fought a pretty tough mini-boss to get a bead at the great serpent shrine. He was tough as balls and I managed to get super lucky on my third attempt and he ended up doing the same moves multiple times in a row letting me posture break him.
I also fought the underwater headless. But when I go through an area I fully explore every possible part of the zones, walking along the edges of pretty much every path to look around for things. I've probably missed some stuff, but I have beaten every mini boss up until this point, and that's where a lot of my beads have come from. My achilles heel is that I have a bad memory, so I oftentimes forget to backtrack to areas when there is something I can't collect right away. Hoping to finish the game with all the beads, but we'll see.
You are way more skilled than me, the guy at the serpent shrine took me no less than 10 attempts before I realized I could stealth him and then another 5 or so after that to kill him and boy was it messy.
Have you gotten to the fight at the top of the castle yet? And if so which one did you get?
No, not yet I haven't. But that's going to be pretty much the next place for me to go. I did see some enemy through the gate at the bottom of the castle which I'm going to look into first, and then make my way to the top. Might not be until tomorrow though. And holy crap you can stealth him? I swear I walked in stealthed but he was aware of me before I could get close. And no, I base my victory on pure luck, and I heard the garage door start to open in the middle of the fight and I knew my wife had arrived with our dinner, so it was a now or never (later) fight.
Edit: You replied while I was in the middle of my edit, so I dunno if you saw my last bit.