There's the statue that allows changing stamina for hearts. Once you have ~10 hearts, you can get the last 3 or so by temporarily switching them with the statue. That helps.
Also, the Trials of the Sword (expansion optional adventure) make the master sword do more damage. It should last longer, as you need to use less strikes with it.
There's a method (speed running glitch) to get the master sword w/o the heart requirement. Do a search for "botw get the master sword early" and you should have lots of step by steps if you ever want to do it.
