There is no perfect posture
I’m often asked “what’s the best posture to sit at my desk.” My answer is that there is no perfect posture - the issue is prolonged postures.
Your body, and especially your spine, wants variety. Sitting perfectly upright all day long with a great ergonomic set up can still lead to discomfort and issues. Changing your position redistributes the forces on your body.
Here are some other ways to increase variety in your work set up, and thus posture, throughout the day:
Change out chairs or the seat height
Change your leg position (put your feet up on a box, sit cross legged, stand with one foot on a box)
Change your sitting posture by leaning forward or back
Put a pillow behind or under you
Change the work surface height
Put your laptop on a box or stand
Change your mouse placement
And, of course, the classic break tips still apply:
Get up and stand or walk every 30/45/60 minutes
Take calls or meetings standing up
Go for a midday walk
Do some stretches throughout the day
I like the strategy of variety as it doesn’t demonize any posture or set you up for failure. It’s not ideal to sustain any posture for hours at a time. Get creative and change it up!