No, Stilly, my new-to-me bed is not adjustable except in the sense that it came with dismountable side rails that are stowed in the basement. It’s just a rectangle of oak with four cross-pieces of hardwood two-by-four (probably maple) for the mattress base to rest on. Its design and technology would be perfectly familiar to a Victorian house-holder.
As for the side rails, they brought me to the conclusion that modern furniture manufacturers believe that beds accommodating only one person are strictly for children. The people who sold me the bedstead told me that their daughter had “grown out of it” when she went off to university. Fact is, lots of people prefer a bed to themselves and don’t need a bed large enough for two adult humans. Watson (cat) prefers to sleep on top of me, anyway!