Obviously everyone will have differing opinions on what is "required" for your home office. I will simply put down what I have, with the understanding that I absolutely love working from home in this environment.
Definitely agree with the comments about a clear separation. It needs to have a door that you can close. That way you "go to work" in the morning and "come home" in the evening. (or whenever) For me since I have a wife and son, it's easiest for me to have a lock on the door. If I'm in there working, I lock the door.
Comfortable sitting environment. This means quality desk and chair. I personally use the Autonomous SmartDesk Business Edition as well as their ErgoChair2. They're super affordable compared to other options for high quality comfortable working conditions.
Excellent monitor(s). I have one large 49 inch ultrawide monitor and it's incredible. I never feel like I don't have the room I need. It's not 4k, as much as I'd love it to be, but it's way more than I need.
Comfortable keyboard. I LOVE my CODE Mechanical Keyboard. Full size, clear switches, it's beautifully simplistic and super comfortable to type on.
Quality headphones. I don't want to hear my family and I don't want to subject them to constantly hearing my music muffled in my office. I use the Bose QC25's and they're amazing, I put them on and I'm able to easily get in the zone.
Also, I personally have two laptops. One is my work-issued laptop, and the other is my personal laptop. I recommend this for a number of reasons. First, you don't have to worry about whether it's okay to do personal projects on a work machine. Second, I don't have all my games, applications, etc., from my personal machine on my work machine. Those are temptations for me when I'm working, so I keep work stuff on my work machine. That's just what works well for me.
Natural light. This is important to my mental health. If I'm working in a place that's dark or poorly lit, I don't feel as good. Natural light is excellent at staving off those feelings.
Some fun things to make the space yours. For myself, I have various Legend of Zelda decorations around my office, as that's my favorite game franchise. Just make it yours.
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