So this s4s is about singing, than any particular set of songs.
A few weeks ago my singing teacher introduced me to a rather bizarre exercise: singing through a straw. Also known as straw phonation, it's a form of SOVT -- semi-occluded vocal tract -- exercise. It's said to have all sorts of benefits, which mainly come from being easier on your vocal folds than straight singing. (Less often mentioned is the fact that it's very quiet, so you can warm up and practice without bothering anyone.)
Anyway, I've been exploring the inside of that particular rabbit hole. It mostly comes down to keeping more acoustic energy inside your vocal tract, where the resonance helps your vocal folds vibrate, rather than sending most of it out your mouth. That, plus the reduced air flow, reduces stress on your vocal folds -- they can relax and let resonance do the work. It's also a resistance exercise -- like exercising in a pool -- for the muscles behind that air flow.
But don't take my word for it -- save the straw from your next coffeehouse drink, and try it yourself.