Nick--

You're right, the more you sing higher notes, the easier it becomes.   


I must respectfully disagree with Seamus on yodeling.   I believe that since you are trying to extend range with a smooth transition, yodeling is not the best approach, since it emphasizes the break.   At least I believe this. Maybe Seamus will tell us how he gets around this problem.

My personal evidence, as I noted earlier, is that when I have recently tried to yodel, I find it impossible to put the break back in.   So as of now, I can't yodel. When a yodel is called for, I whistle instead.

I have a lousy range--1 1/2 octaves.   But falsetto doubles it.   I've been able to smooth over the break so that it is virtually not noticeable. With all the singing I do, I've developed a quite strong and precise falsetto.   And I've been singing all kinds of music for decades in all sorts of groups: classical, doo-wop, country, bluegrass, sea chanteys, jazz, Carter Family, Irish, etc. And in all sorts of groups::   1 on a part, 2 on a part, 18-20 in the group, 40-45 in the group, 180 in the group.   In a church choir in which I was the paid bass section leader, I was also called on from time to time to sing tenor or even alto. I was recently asked to sing tenor for a gig in a small group in which I was formerly the main bass.

This is all just by way of asserting that falsetto is very useful.

Without falsetto, I would never have been accepted into any group.

If I were asked for advice in extending range, I'd just say: sing as much as you possibly can--all the time ( but not loud in the higher ranges).   I figure I owe my range to the Beach Boys, since I've been singing in the car with them for, again, decades. Don't ever push for notes, but try to sing with the higher voices--higher than you're used to singing.   (Franki Valli is taboo, however--they must have done something to his voice in the studio.--don't try it.)

It helps, of course, that I really like the Beach Boys. Maybe you'd rather pick some other group with some high voices. And don't try to sing as loud as the part you're following, just try to hit the same notes--unless it seems too much of a strain--then back off.

But it really is liberating to be able to switch into falsetto unnoticed--and very worthwhile.