I buy a medium set (.013-.056) for the primary set and use the first four strings from a light set (.012-.054) for the octaves. Tuned down three half steps, it is about the same tension as a regular extra-light (.010-.047) 12-string set tuned to pitch.
Thanks for checking in, Teja.
I have that video saved as a favorite on my YouTube page. I agree, sometimes when I listen to Ralph Towner or Michel Gentils (to name a couple), I wonder if I should re-think my approach. Then when I actually try it, it doesn't sound right. I guess it is what you are used to.
I really shouldn't do this, because Al Petteway might see it, but here is my latest. Sligo Creek on a 12-string, DADGAD tuned down to B: