is it the ultra 20 from old that is only good to 32* or the new true to rating one?
If it needs to get to 32* with no insulated clothing it has to be Climashield XP 5oz, 20* go with 7.5oz (5oz + 2.5oz).
As for materials owfinc.com and thru-hiker both have a good .9oz nylon. Thru-hiker calls theirs momentum 90. Both make a warmer bag than standard 1.1oz as they have better dwr and calandering (sp?). Those materials will be high quality like the shell of the unltra 20 vs some generic 1.1 that does work but wont be as warm in the long run.