Along these lines, I have been thinking that a "spa day" is mostly a mindset, and it can be most days!
An electric kettle heats up water to boiling in a minute, add the hot water into a little tub, and soak your feet wherever you are.
Automatic back and foot massagers are a cheap investment and feel great.
Applying body oil after the shower is good for the skin and makes it feel more comfortable to wear.