I continue to recommend considering a hospital bed that you can place adjacent to yours a couple of inches apart. In addition to adjusting the height and head/feet angles, you can swap out mattresses and overlays as needed, and have room on every side of the bed [assuming you don't use a headboard or footboard] for his care, changing linens and transfers.
With a split king, you lose at least one side of the bed and maneuvering room for the Hoyer and pivots. I understand the lure of the adjustable bed, I just don't want anyone who can't afford it to have to pay twice, if it doesn't work out. Medicare does contribute to the hospital bed.
With linens on a boardless frame, a hospital bed really doesn't look like one, and the adjacent bed shouldn't be that much these days (I am currently sleeping well on a $50 frame, $150 mattress, $200 overlay).
For context, Larry got out of bed every day until his last week, so I am not saying this from the perspective of being "confined to bed," but rather for the considerable care that must be given there.