I put a Leatherman in its pouch or something similar in my right front pocket, laying flat on the bottom, far left corner, and then sit down. This bulge holds up and keeps the bass from feeling like its sliding off my leg even if I put my foot on the floor for a bit from the stool footrest or otherwise squirm around.
If it's a mostly seated gig, or a marathon practice session, I'll also fold up a shop rag twice and put it in my pocket and smooth it out. It makes for a nice pad and air can get in there.
Oh, watch using your key ring in your pocket, find something else. Nothing like playing and during a break you hear "some jerk's" car alarm going off out in the parking lot. And then you figure your remote fob panic button got pushed and it's you!!! It only happened twice before the Leatherman.
The footrest on my stool was a bit low, so I screwed on a piece of 2x4, wrapped it in a shop rag and put a bunch of black duct tape on it for padding. Just add more as it wears through. It's fairly comfy, but I need to get a cheap padded stool seat cover for it, especially now that I'm also playing keyboard a lot. The thing in my pocket also keeps the bass from hitting the keyboard. Bonus hint: put some double-sided carpet tape down under a seat cover so it doesn't squirm around on you.
I always wear a loose strap when sitting. Free insurance.
The right side of his body looks "slouched" and I wonder if maybe that's not the best ergonomics.
When you see a posed picture and not a real live-action shot, the photographer probably told the subject how to sit for the best image, and usually it feels unnatural. Not the best idea to use as an example.