You're gonna be looking at monitor arms for the monitor. There's plenty on amazon. Just be sure to check (a) the weight limits, (b) the range of how far it can tilt downwards so you can see it while reclined/laying down, and (c) the reviews to make sure it's actually okay. To hold a keyboard. . . if you're in bed, it can easily go on your lap. I recommend a trackball mouse -- instead of moving the mouse itself (which can be difficult on things such as bedding), you move the embedded ball around to move your cursor.
My current set up right now is a computer cart/mobile workstation. It's on wheels, with my desktop on the lowest level, and on the top I've got a monitor arm attached to the side of the tabletop. When I want to use it, I roll the cart to the side of my bed, swing the monitor over, put the keyboard in my lap and trackball mouse right next to me as I recline on a bunch of pillows. The desktop pc provides enough counterweight for the monitor, so I'm not worried about it tipping over, and having it on wheels means it's easier for me to move it around/out of the way when I'm not using it. If you'd like, I can dig up the amazon links for the cart that I got, along with my current monitor arm.
Also: took a quick look at the original post and it seems OP used this workstation: https://www.amazon.com/AW-Rolling-25x22x69-Computer-Workstation/dp/B017VMYMY4
and this monitor arm: https://www.amazon.ca/gp/product/B0779BHZCG?psc=1
(The thread where they discuss their build can be found here, if you'd like to further reference it: https://www.reddit.com/r/ChronicPain/comments/lu06z2/bedridden_battlestation/gp3pumj )
All the places I've ever worked like that had some sort of mobile/rolling cart like this: https://www.amazon.com/AW-Rolling-25x22x69-Computer-Workstation/dp/B017VMYMY4