It really should be simple, shouldn't it?
As it happens, Mariah of Comet Camper Blog fame/infamy actually teaches a class from time to time on the nuts and bolts of how to downsize and simplify your life so you can be a happy camper in your tiny house, camper, or other small living space not unlike a boat. From what I hear it is a very good class and well worth taking. From where I sit most of the really good living on a boat advice I've come across on the web in the last year or so has come from the Comet Camper Blog so you might want to bookmark it and give it a read on a regular basis... She does make a heck of a lot of sense.
On the other hand, if you wanted to take a class to learn about how to cruise and live on a boat you'd find that you'd actually be taking a class not so much about simplification or downsizing but mostly about buying stuff...
Expensive stuff as it happens. Lots of expensive stuff.
Just the other day I read an article that used words like simplify, downsize, and make do with less, but the real subject seemed to be more about making room for a new bigger watermaker, an interior makeover, and a proper SSB/Ham radio installation which is hardly downsizing or simplifyiny but all about making things less simple and spending money.
Maybe it's more than time that we look a lot more closely about the words we actually use...
SIMPLIFY : to make simple or simpler: as
a) to reduce to basic essentials
b) to diminish in scope or complexity : streamline (was urged to simplify management procedures)
c) to make more intelligible : clarify
Not exactly rocket science is it?