> It is very difficult for me to achieve that posture while sitting in a chair - the keyboard and mouse need to be in your lap, basically.
I found that I could manage that posture with a sufficiently adjustable chair and height-adjustable desk. I adjust the chair until it provides the correct height off the ground (feet touching, hips at the right angle), then adjust the desk and the chair arms until the chair arms go just over the edge of the desk, allowing arms to rest on them and use the keyboard naturally.
(Also, I use a USB ThinkPad keyboard, so my mouse is on home row, not off to the side.)
Personally, I can't get into the 'proper' position when sitting at all, my arms are too long. I'm 6'2" ~190lb and when sitting in an ergonomic chair with proper posture, my elbows are within an inch of the top of my quads. Attempting to sit properly at a desk requires my quads to be jammed into the underside of the desk which is horribly uncomfortable. The only thing that is comfortable when sitting is raising the desk up a lot and extending my arms way into the desk to the point where my arms are nearly at shoulder height.
> I use a USB ThinkPad keyboard, so my mouse is on home row, not off to the side.
I switched a tenkeyless keyboard for the same reason... my mouse is now a lot closer to the center of my body and this has reduced shoulder strain immensely.
I found that I could manage that posture with a sufficiently adjustable chair and height-adjustable desk. I adjust the chair until it provides the correct height off the ground (feet touching, hips at the right angle), then adjust the desk and the chair arms until the chair arms go just over the edge of the desk, allowing arms to rest on them and use the keyboard naturally.
(Also, I use a USB ThinkPad keyboard, so my mouse is on home row, not off to the side.)