maybe this? https://getmechanism.com/products/gaming-pillow

You could try the Steam Deck Case to support the Steam deck while you hold it. This is, what I do sometimes.

I just use a hard pillow on ma belly

I use a pair of XREAL Nreal Air AR Glasses with my steamdeck. I dont even have to look at the screen. Its nice.

Get a wireless controller, a cheap projector and project the screen on the ceiling, so you can look straight up without bending your neck! I know it sounds a bit absurd, but I actually had a similar setup for watching movies (I tied the projector to the back of the bed post)

I used to have a ceiling mounted tv with a bit of tilt when I lived in literally one room with no space for a desk. It was literally just a vesa bracket bolted to the tv and a 2x4 wedge frame screwed into the ceiling joists. When I left that place I just balled up toilet paper mushed into elmers glue and stuffed it into the holes.

I use a magic arm originally meant for photography work, e.g. holding a reflector or camera highlight flash. Brand mostly doesn't matter, but at the weight of a Steam Deck, you don't want garbage. Specifically, I use a Newer because I've had great luck with their stuff has been consistently good over the years. To hold the Deck, I have a Ram Mounts tablet X-Mount, which keeps the vents and buttons juuust accessible. I usually use a Bluetooth game controller. Works great anywhere I can clamp the base.

Is it weird that I never, like never ever, game in bed?

Closest I get is in a hammock while camping I guess. For that I just use my XReal One XR glasses. Pretty expensive but it's also great for plane/train rides and working on places too small for a large monitor setup

You mentioned seeing the mechanism pillow, they actually offer 3d print models for a lot of their connectors and mounts. There are several options for how you could use them, I've seen people do a long arm monitor mount that they can swing out over their bed and clip the deck to.

A cylinder or triangle elongated semi-soft object you can lay lengthwise on your torso and balance the steamdeck at a pivot point on. Think foam yoga roller, stiff bolster pillow or headboard wedge pillow or something where you can rest but still pivot the steam deck around a central point. A large hardcover book or two with something on top also works. Just make sure it narrows near the pivot point/top so you can lay your arms comfortably on either side.

A basic clamshell camping chair if it is stiff enough works as a decent platform to use the steam deck "laptop style" with a bluetooth keyboard especially if you lay a thin wide book behind the steam deck as a backing to prop it up.

I usually put my Deck on my belly. Thank God for adipositas!

But I also got a monitor arm to mount my PC monitor over my bed. I'm planning to play with a Steam Controller and maybe down the line with the Steam Frame controllers to be able to keep my hands independent of each other.

I like the idea of a ceiling mounted screen (as mentioned by someone else), but get yourself a dock and then you just need to hold a joystick.

It's how I use my deck, but also with headphones (I don't have a sound bar and screen has nou audio output)

I can't get past the daily routine of having 2 uninterrupted hours of gaming and TV watching with the Mrs every night. What luxury. By the time we get the kids on bed, cleaning done and prep for the next day; theres little time left and it is often spent trying to catch up with work emails or home admin.

I haven't tried it on the Deck yet, but expect it to work:

Nintendo Switch Joy-Cons. Lean the Deck (or Switch) on its side on something, such that with your head on the pillow you can look at it. With one joy-con in each hand, you can reposition your arms however you want and independently of each other.

This method with Ace Attorney games on the Switch is my sleeping pill. Works amazingly well for me. After I finish my current Ace Attorney game, I plan to finally try it with the Steam Deck and a different visual novel.

Foreseeable caveat: charging the joy-cons will be annoying. If you put them in a Switch to charge (which is my only charging solution right now), they get paired to it automatically and will need to be re-paired with the Deck.

Also, leaning the Steam Deck on its side won't be as easy as it is for the Switch. Might have to improvise something for that.