Some of us have skin that is healthier if we soak a long time than if we shower.
At many retail sites (e.g., Walmart) you can find many inflatable barrel style bath tubs and folding bath tubs, by searching for “inflatable tub” or “folding tub” or “spa” or “sit bath”. Basically they are updated versions of the barrel bath tubs that were used in colonial days. The smallest adult-size ones are about 70 cm high x 70 cm diameter. Adults kneel or sit inside.
(I’m not sure I need this, but on the deluxe side, some have lids, that help keep the heat in. Some have heaters, though they require a lot of electricity. Some pumps to create a whirlpool effect are available.)
Regardless 70x70 cm is a lot of water - around 70 gallons.
Is there such a thing as a conformable tub? Something like a sturdy waterproof bag like structure, with a standing frame, that conforms to the body, so you can use much less water?
If no, are there any really sturdy waterproof bags that could be easily adapted to the purpose?
If the answer is no, are any of the standing cylindrical ones reasonably sturdy? I’ve seen a lot of online ratings that say at least some of them can break or leak.