I used one like this when I had surgery and couldn’t lie down. I really like it.
Not helpful now but it might be worth trying a pillow wedge to lay down with. That way you can rest but still be laid back a little to prevent GERD from flaring up.
This is mine: https://www.amazon.com/gp/product/B00U6HMK78/ref=ppx\_yo\_dt\_b\_search\_asin\_title?ie=UTF8&psc=1
My SO has stage 4 as well and just had robotic excision surgery, still recovering now.
Other than what you listed, got her this wedge pillow to stay elevated post surgery, and it drastically reduced her pain when sleeping and is helpful for sitting up in bed. I’d call that second most important item after her heating pad.
On another note, hang in there and make sure you keep an eye on everyone’s emotional health. I know this sub (and endo in general) can be scary as a partner. The emotional side of things has been toughest to help her with, but I’ve found lots of distraction is helpful. Stocked up on video games and books in my gf’s case.