Electric stored water systems can be quite compact.
There are wall mounted 90L unvented mains pressure systems, 3kW
powered, with about 80min recovery time. They are a rectangular box on
a wall, look a bit like a gas boiler, self-contained and since mains
pressure can be situated anywhere you like. Integral frost-stat, clean
"white appliance" as it were.
Without stored water you are onto a non-starter for filling a bath,
but that need not necessarily be the "600x600x1500mm" space for
conventional CW tank & HW tank arrangement.
I would like one for my mother re 1-stop solution, but one wall is
cinderblock & the other the chimney so I am loathe to allow anyone to
screw anything to it.