To be clear, is your cozy one that fits around the pot, or is it a sleeve that the freezer bag goes into? I like the latter, one that holds a quart sized freezer bag. This works great solo hiking, or in fact can work good for a couple of people sharing food so long as their caloric intake isn't super high (a quart F.B. was right for me alone when thru-hiking, but would be enough for my wife and I together on a more normal trip).

I bought my cozy from Sarbar's site.

Heating water twice: my personal solution to that is to simply not do it, no hot drink, but each to their own there of course. A couple times this year my wife joined me on my long hike and I heated water twice (for two dinners), didn't seem to be a problem.

I can't think of any technical approach that allows you to heat more water than a given pot size will hold (!), so IMO it ultimately comes down to a personal trade-off based on your hiking style and what you want to optimize. The vectors of investigation for me would be (a) attitude adjustment to be happy with less water or heating twice, (b) a big but light pot you can strap on the outside like a tinker ...