In Japan most households have a small, deep bath tub with a shower over, so you get clean in the shower then have deep soaks for joint health. They are usually just like a normal bathtub but shorter and deepr, so you kind of sit up to your shoulders in hot water. I notice more firms in the UK are now offering these, so if it's really for health and not for a garden feature you might think about replacing your existing bath. Here's one such firm, but there are many others.
http://www.cabuchon.com/deep-soaking-bath-tubs/