I can relate to your issue. Twelve strings can add up to a great deal of resistance - so it definitely helps to go as light as possible. And with a 12 string, the sound you are going for is not necessarily dependent on boomy volume out of your acoustic strings. It's more of a chimey chorus effect and with 12 strings, you get more volume inherently.
Having said that, I still prefer to use either a phosphor bronze or 80/20 bronze for all of my wound strings on all of my acoustic guitars. The bronze wound strings are only available as acoustic strings because they resist the magnetic field found in electrics. And they sound much better acoustically than nickel wound electric strings. I know this because I had an acoustic with a magnetic pickup and I tried several brands of electric strings to get more amplified volume from my wound strings. They did sound louder when plugged in. But they sounded very dull and dead (all brands) acoustically.
But the plain steel strings (unwound) are made from the same material for electric or acoustic. So I will sometimes buy a set of super slinky electric strings to rob the set of the thinner plain steel strings and mix them with a light acoustic bronze set.
A better option if you have time to wait on the strings to arrive in the mail, is order individual strings from a company that sells strings on-line. I personally use Just Strings Just Strings Website. They carry a wide variety of strings from all the major manufacturers.
It is common in a 12 string set for the octave g string to be the same gauge or even slightly thinner than the high e pair. However, I don't recommend going any lighter than .08 on any guitar. Any thinner than that and it's like playing a thin thread and they tend to break easily.
Another option you might want to consider until you get your calluses built back up - is to go with soft feeling silk and steel strings such as the ones found in this 12 string set 12 String Soft Set. In a "silk and steel" set, all of the wound strings have a polyester wrap beneath the bronze outer wrap that acts like padding - making them very soft to the touch. I know they won't sound as bright or loud as regular wound strings, but playing them for a month or two (until it's time for a string change) might minimize the pain involved in the callous building process. To make this set even easier to play, order some .08 and .10 plain steel individual strings to swap out the .09's and .12 plain steel strings in this set. Save the .09's for later when you build up your callouses and want to go to slightly heavier strings.
Many folks (myself included) tune their 12 strings to D#/Eb (half step flat). The theory is that tuning flat results in less tension on the neck with 12 strings tugging against the truss rod. I don't know if the neck of most decent 12 string guitars would have a problem coping with standard tuning, but tuning a half step flat does mean less pressure is required to fret the strings. And it's easier to hit the high notes in the songs I sing.
One other thing to note, is that a lower action will make the guitar easier to play. On my 12 strings, I like to get the action as low as possible and still remain buzz free. I have tried to play 12 string guitars with a high action and find it impossible for me to cleanly play any barre chord (even with light strings). So the setup of your guitar can be as big a factor as string gauge.
I hope your new 12 string provides untold hours of enjoyment as you continue to get used to playing it and discover the magical sounds it can make.